the nearby environment of seyfert galaxies: a comparative study marcel l....

THE NEARBY ENVIRONMENT OF SEYFERT GALAXIES: A COMPARATIVE STUDY

Marcel L. VanDalfsen

A thesis submitted to the Faculty of Graduate Studies

in partial fulfillment of the requirements

for the degree of

Graduate Program in Physics and Astronomy

York University

North York, Ontario

September 1997

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The Nearby Environment of Seyfert Galaxies: A Comparative Study

by Marcel L. VaxDalfsen

a thesis subrnitted to the Faculty of Graduate Studies of York University in partial fulfillment of the requirements for the degree of

Master of Science

Permission has been granted to the LIBRARY OF YORK UNIVERSITY to !end or sel1 copies of this thesis. to the NATIONAL LIBRARY OF CANADA to microfilm this thesis and to fend or sel1 copies of the film, and to UNIVERSITY MICROFILMS to publish an abstract of this thesis. The author reserves other publication rights, and neither the thesis nor extensive extracts from it may be pnnted or otherwise reproduced without the author's written permission.

Abstract

The question of whether active galactic nuclei (AGN) have more nearby companion

galaxies than "normal" galaxies is important in providing evidence for the origin of

activity in galactic nuclei, e.g., by tidal triggering. The "interaction hypothesis" sug-

gests that Seyfert galaxies should have an exces of cornpanions which may tidally

trigger nuclear activity. By examining the host galaxy properties and nearby envi-

ronments (5200 kpc) of both Seyfert galaxies and a control set of non-active galaxies,

the large-scale differences between Seflerts and non-active galaxies can be determined

and the interaction hypothesis can be tested.

The two datasets were chosen from the Center for Astrophysics (CfA) spectro-

scopic sample, and were carefully matched in morphological type, absolute magni-

tude and redshift. Upon andyzing the properties of the 32 Seyfert galaxies and 49

control galaxies, there was indication that a fair cornparison was in fact being made

between the two samples. Counts of optical companion galaxies around the hosts and

their magnitudes reveal that the Seyfert hosts occupy environments similar to the

control hosts. There are a h a similar number of disturbed morphologies and light

asymmetries in both samples. These results inàicate that interactions rnay not be

the sole mechanism for initiating activity in Seyfert galaxies. Results which show the

similaxity of the environments of the Seyfert galaxies and the control galaxies will be

presented in the body of the thesis, dong with the techniques used to acquire these

results.

Acknowledgment s

1 would like to thank my supervisor, M.M. DeRobertis, for his advising during my

graduate studies, and for his excellent teaching during my undergraduate years. 1

would dso like to thank Marlene Sherman for al1 the administrative details she took

care of while 1 was at York. Thanks also go to my parents for their suppoa and love

during al1 my studies.

Monetary thanks goes to OGS; computationd thanks goes t o e ~ u n Microsysterns.

I would also like to thank whoever designed Unix (a beautifid operating system),

and to Donald Knuth and Leslie Lamport for T)jX, w, and (I'm one

of the people who actually Iike this typesetting program). This research has made

use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet

Propulsion Laboratory, California Institute of Technology, under contract with the

National Aeronautics and Space Administration.

Thanks to MadDog Murphy for the nick name of Kool Mo V. And for al1 of you

who said 1 couldn't put Klingon in my thesis, here it is: Q7k. 1 would

like to thank al1 my couch (and bar) buddies for their (la& of) support, humour and

wit, arnong others: Ryan Ransorn the greatest pitcher (Ransom IN?), Rob Metcalfe,

Mauro (Murph) Aiello, Robert Ross (aiien boy), Me1 Blake, Henry (Hank) Lee, Naomi

Black, Leanna, Curtis Krawchuk, Dave DelRizzo (%O), M. J., Sabrina, Veronica, and

Renée Desmond.

No baby Seals were h m e d in the production of this thesis!

This thesis wil1 self-destruct in 10 seconds.

On a final note in memory of J.R.R Tolkien:

Contents

Abstract

Acknowledgment s

List of Tables

List of Figures x

1 Introduction 1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Overview 1

1.2 Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

. . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 Spiral Galaxies 3

. . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Active Galaxies 4

1.2.2.1 Active Galactic Nuclei . . . . . . . . . . . . . . . . . 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Seyfert Galaxies 6

. . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Properties and Types 6

1.3.1.1 Seyfertl . . . . . . . . . . . . . . . . . . . . . . . . 7

. . . . . . . . . . . . . . . . . . . . . . . . 1.3.1.2 Seyfert 2 8

. . . . . . . . . . . . . . . . . . . . 1.3.1.3 Fractional Types 8

1.3.2 Unified Mode1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

. . . . . . . . . . . . . . . . . 1.3.3 Interaction/Merger Hypothesis 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.4 Objective 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Thesisobjective 12

. . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.1 Previous Work 13

2 Observations and Reduction Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Observations

. . . . . . . 2.2.1 Selection of Seyfert Galaxies and Control Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2-2 CCDs

. . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Data Acquisition

. . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Preliminary Reduction

. . . . . . . . . . . . . . . . . . 2.3.1 CCD Pre-Processing in IRAF

. . . . . . . . . . . . . . . . . . . . . 2.3.2 Photometric Calibration

. . . . . . . . . . . . . . . . . . . . . 2.3.3 Host-Galaxy Magnitudes

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Image Analysis

. . . . . . . . . . . . . . . . . . . 2.4.1 Image Statistics and Editing

2.4.2 Elliptical Isophotal Analysis . . . . . . . . . . . . . . . . . . . 2.4.3 Surface Brightness Profile Fitting . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . 2.4.4 Cornpanion Galaxy Searching

. . . . . . . . . . . . . . . 2.4.5 Unsharp Masking and Morphology

2.4.6 Galaxy Parameters and Statistics . . . . . . . . . . . . . . . .

3 Discussion of Seyfert Galaxies 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 The Galaxies

. . . . . . . . . . . . . . . . . 3.3 Summary of Seyfert Galaxy Properties

4 Discussion of Control Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Analysis

. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 The Galaxies . . . . . . . . . . . . . . . . . 4.3 S u m m q of Control Gdaxy Properties

5 Cornparison Between Seyfert and Control Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction

. . . . . . . . . . . . . . . . . 5.2 Distribution of Host Galaxy Properties

. . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Host Galaxies

. . . . . . . . . . . . . . . . 5.2.2 Distribution of Fitted Parameters 117

. . . . . . . . . . . . . . . . 5.3 Distribution of Environmental Properties 121

5.3.1 Properties Derived from Cornpanion Galaxy Data . . . . . . . 121

. . . . . . . . . . . . 5.3.2 Host Gdaxy Morphologicd Disturbances 129 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Sumrnary 132

6 Conclusions 133

Bibliography 138

A Prograrns Used for Analysis 141

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.1 IRAF Packages 141 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A . l . l Imexamine 141

. . . . . . . . . . . . . . . . . . . A.1.2 STSDAS/Isophote/Ellipse 142 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.1.3 Imedit 143

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.1.4 Imarith 144

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.1.5 Gauss 144

. . . . . . . . . . . . . . . . . . . . . . . . . A.2 User-Supplied Programs 144

. . . . . . . . . . . . . . . . . . . . . .4.2.1 galprof and sp l i tprof 145 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A. 2.2 raddist 146

B Ellipticity and Position Angle Plots 148

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.1 Seyfert Data Set 148

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.2 Control Data Set 148

... Vll l

List of Tables

Luminosities of various objects . . . . . . . . . . . . . . . . . . . . . . 5

Apparent magnitude transformation coefficients . . . . . . . . . . . . 21

Basic properties of Seyfert galaxy dataset . . . . . . . . . . . . . . . . 60

Seyfert galaxy image statistics . . . . . . . . . . . . . . . . . . . . . . 61

Ellipse parameters for the Seyfert galaxies . . . . . . . . . . . . . . . 62

surface-brightness profile parameters for the Seyfert galaxies . . . . . 63

surface-brightness profile parameters for the Seyfert galaxies. method II 64

Distance/luminosity parameters for the Seyfert galaxies . . . . . . . . 65

Basic properties of control galaxy dataset . . . . . . . . . . . . . . . . 102

continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Control galaxy image statistics . . . . . . . . . . . . . . . . . . . . . . 104

continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Ellipse parameters for the control galaxies . . . . . . . . . . . . . . . 106

continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

surface-brightness profile parameters for the control galaxies . . . . . 108

continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Distance/luminosity parameters for the control galaxies . . . . . . . . 110

continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Seyfert hosts: ban. rings and distortions . . . . . . . . . . . . . . . . 130

Control hosts: bars. rings and distortions . . . . . . . . . . . . . . . . 131

Frequency of bars. rings and distortions . . . . . . . . . . . . . . . . . 131

List of Figures

. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 An Elliptical galaxy 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 A Spiral galaxy 2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 A Seyfert galaxy 2

. . . . . . . . . . . . . . . . . . . . . . . . . Sample Seyfert spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AGN illustration

. . . . . . . . . . . . . . . . . . . . . . . . . . . . Seyfert orientation

Detector Quantum EfEciency (DQE) plot for Tek2048 . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample deblending of NGC 5541, 1

. . . . . . . . . . . . . . . . . . Sample deblending of NGC 5541, BI

. . . . . . . . . . . . . . . . . . Sample deblending of NGC 5541. Al

. . . . . . . . . . . . . . . . . . Sample deblending of NGC 5541. A2 . . . . . . . . . . . . . . . . . . . . 1-D example of unsharp-masking

Sample unsharpmasked image of NGC 5289 . . . . . . . . . . . . . Sample unsharp-masked image of NGC 3968 . . . . . . . . . . . . . Sample unsharp-masked image of NGC 4172 . . . . . . . . . . . . . Sample unsharp-masked image of NGC 6111 . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . Intensity contour map of Mrk 0231

. . . . . . . . . . . . . . . . . . . Radial profile and fit of Mrk 0231



. . . . . . . . . . . . . . . . . . . Intensity contour rnap of Mrk 0471





. . . . . . . . . . . . . . . . . . . Radial profile and fit of Mrk 0817 38

. . . . . . . . . . . . . . . . . . . Intensity contour map of Mrk 0841 39

. . . . . . . . . . . . . . . . . . . Radial profile and fit of Mrk 0841 39 . . . . . . . . . . . . . . . . . . Intensity contour map of UGC 06100 40

. . . . . . . . . . . . . . . . . . Radial profile and fit of UGC 06100 40

. . . . . . . . . . . . . . . . . . Intensity contour map of UGC 08621 40


. . . . . . . . . . . . . . . . . . Intensity contour map of NGC 3080 41

. . . . . . . . . . . . . . . . . . . Radial profile and fit of NGC 3080 41





Intensity contour map of NGC 3516 . . . . . . . . . . . . . . . . . . 43

Radial profile and fit of NGC 3516 . . . . . . . . . . . . . . . . . . . 43















Intensity contour rna~ of NGC 4388 . . . . . . . . . . . . . . . . . . 49





. . . . . . . . . . . . . . . . . . lntensity contour map of NGC 5273 51


. . . . . . . . . . . . . . . . . . Intensity contour rnap of NGC 5283 52

. . . . . . . . . . . . . . . . . . . Radiai profile and fit of NGC 5283 52





Intensity contour map of NGC 5674 . . . . . . . . . . . . . . . . . . 54 Radial profile and fit of NGC 5674 . . . . . . . . . . . . . . . . . . . 54










. . . . . . . . . . . . . . . . . . htensity contour map of UGC 05734 67








. . . . . . . . . . . . . . . . . . Irtensity contour map of UGC 10407 70



. . . . . . . . . . . . . . . . . . . . Intensify contour map of IC 875 71

. . . . . . . . . . . . . . . . . . . . . Radial profile and fit of IC 875 71

. . . . . . . . . . . . . . . . . . . . Intensity contour map of IC 1141 72

. . . . . . . . . . . . . . . . . . . . Radial profile and fit of IC 1141 72
















Radial profile and fit of NGC 4048 . . . . . . . . . . . . . . . . . . . 78 . . . . . . . . . . . . . . . . . . Intensity contour map of NGC 4088 78



Radial profile and fit of NGC 4172 . . . . . . . . . . . . . . 79 . . . . . . . . . . . . . . . . . . Intensity contour map of NGC 4224 80








xiii






















Radia1 profile and fit of NGC 5690 . . . . . . . . . . . . . . . . . . . 90











xiv




















Radial profile and fit of NGC 6196 . . . . . . . . . . . . . . . . . . . 100 Intensity contour map of NGC 6764 . . . . . . . . . . . . . . . . . . 101


Distribution of host redshift . . . . . . . . . . . . . . . . . . . . . . . 114

Distribution of host distances . . . . . . . . . . . . . . . . . . . . . . 115

Distribution of host apparent magnitudes . . . . . . . . . . . . . . . 115

Distribution of host absolute magnitudes . . . . . . . . . . . . . . . 116

Distribution of host eliipticities . . . . . . . . . . . . . . . . . . . . . 116

Distribution of disk scde radii . . . . . . . . . . . . . . . . . . . . . 117

Distribution of bulge effective radii . . . . . . . . . . . . . . . . . . . 118

Distribution of disk surface brightness . . . . . . . . . . . . . . . . . 119

. . . . . . . . . . . . . . . . Distribution of bulge surface brightness 120

. . . . . . . . . . . . . . . . . . Number of companions around host 122

5.11 Distribution of companion separation distances . . . . . . . . . . . . 123

5.12 Distribution of companion position angles . . . . . . . . . . - . . . . 124

5.13 Distribution of companion apparent magnitudes . . . . . . . . . . . 125

5.14 Amag between host and companion . . . . . . . . . . . . . . . . . . 126

5.15 Distribution of companion absolute magnitudes . . . . . . . . . . . . 126

5.16 Cornpanion galaxy luminosities . . . . . . . . . . . . . . . . . . . - . 127

5-17 Cornpanion galaxy tidal parameters . . . . . . . . . . . . . . . . . . 127

5.18 Host galaxy tidal parameters . . . . . . . . . . . . . . . . . . . . . . 128

B.1 Ellipticity (Eps) and position angles (PA) of Mrk 0461, Mrk 0817 and

NGC3080 . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . 149

B.2 Eps and PA of Mrk 0471, UGC 06100 and NGC 3516 . . . . . . . . 150

B.3 Eps and PA of Mrk 0231, NGC 3362, NGC 5548 and NGC 6814 . . 151

B.4 Eps and PA of Mrk 0789, NGC 3786, NGC 5252 and NGC 5347 . . 152

B.5 Eps and PA of NGC 3982, NGC 4151, NGC 4253 and NGC 5695 . . 153


8.7 Eps and PA of NGC 3718, NGC 4051, NGC 4235 and NGC 4388 . . 155

B.8 Eps and PA of Mrk 0841, UGC 08621, NGC 5273 and NGC 5283 . . 156

B.9 Eps and PA of IC 875, NGC 3492, NGC 6155 and NGC 6196 . . . . 157


B.ll Eps and PA of UGC 09295, IC 1141, NGC 3169 and NGC 6030 . . . 159

B.12 Eps and PA of UGC 07064, UGC 10097 and NGC 3938 . . . . . . . 160

B.13 Eps and PA of NGC 4045, NGC 6001 and NGC 6085 . . . . . . . . . 161







B.20 Eps and PA of UGC 05734, NGC 4472 and NGC 6764 . . . . . . . . 168

B.21 Eps and PA of UGC 11865, NGC 5603, NGC 5644 and NGC 6126 . 169

Chapter 1

Introduction

1.1 Overview

This thesis will compare the environmental and host-galaxy properties of a sample

of Seyfert galaxies with a control sample of non-active spiral galaxies. In order to

introduce this study, 1 will provide general background information on galaxies in

Section 1.2, discussing relevant properties of both spiral galaxies and active galaxies

dong with their "central engines". Section 1.3 will then provide detailed information

about Seyfert galaxies and their properties. The Seyfert discussion will then lead into

a description of the Unified Mode1 of active galaxies (of which S e m galaxies are

a member) in Section 1.3.2 followed by Section 1.3.3 which describes the triggering

mechanism via the interactionlmerger hypothesis. Finally, Section 1.4 will describe

the objective of this thesis including a discussion of previous work in this field. Fol-

lowing this introductory chapter, Chapter 2 will describe the reduction and analysis

techniques used in this study. Chapters 3 and 4 will present the results for both the

Seyfert and control samples respectively. Chapter 5 will then discuss the comparison

of the Seyfert and control-sample environments, followed by conclusions in Chapter 6.

1.2 Galaxies

Galaxies are the largest individual assemblages of stars, gas, and dust in the uni-

verse and have been recognized as such only since the 1920s. During this period,

Edwin Hubble devised a classification scheme consisting of elliptical, spiral, and ir-

regular galaxies. Since then other (sub)types of galaxies have been discovered such as

lenticulars, dwarfs, and active galaxies, and more detailed classification schemes have

been devised (e-g., de Vaucouleurs 1959). The following presents an example of an

elliptical, spiral, and active galaxy: Figure 1.1 shows a fairly typicd elliptical galaxy,

M84, which is a member galaxy of the Virgo cluster; note the lack of structure in the

galaxy. Figure 1.2 shows a face-on normal spiral galaxy, M74, found in Pisces; note

the nucleus and the spiral a m s that wind out from the core. Figure 1.3 presents a

well studied active galaxy, the Seyfert galaxy NGC 4151, which is a spiral galaxy that

dso contains a very bright star-like nucleus. In the following sections, spiral galaxies

and active galaxies (with an emphasis on Seflert galaxies) will be discussed.

Figure 1.1: Elliptical Figure 1.2: Spiral galaxy Figure 1.3: Seyfert gdaxy M84 M74 Galaxy NGC 4151

1.2.1 Spiral Galaxies

Typical spiral galaxies consist of several components. The most notable components

are a spheroidal bulge of stars and an exponential disk of stars (as well as gas and

dust). A halo of old stars and globular clusters also surrounds a spiral galaxy (the

halo may be an extension of the bulge). A large spiral galaxy has a diameter of

30 kpc and a thickness 2-5 kpc perpendicular to the plane of the disk. The bulge

is made pnmarily of older, red stars whieh formed early in the galaxy's history.

Spheroidal bulges of spiral galaxies are very similar to elliptical galaxies, in which the

intensity or surface-brightness profile has been modeled by a number of functional

forms including those devised by Hubble (1930), King (1966), and de Vaucouleurs

(1948). Surface Brightness is a rneasure of brightness (intensity) per unit area. In

general, a de Vaucouleurs's r1I4 law is the most commonly used fonn for bulges (see

Section 2.4.3 for the mathematical form of this law). The disk component of a spiral

galaxy contains young stars, and material in the form of gas and dust. The intensity

profile of the disk has been modeled well as an exponential by Freeman (1970) (see

Section 2.4.3 for the equation), though there can be significant deviations from this

law due to the presence of spiral m s , bars, rings, discrete star formation regions,

and so on. One of the more spectacular features of a spiral galaxy is its spiral arms

which contdn enhanced star-formation regions and young, luminous O and B type

st am.

Bars and rings are common 'tazimuthal asymmetries" which may also occur within

a spiral galaxy. A bar is an elongated region of stellar and interstellar material

centered on the nucleus with a nearly constant intensity profile along its major axis.

Bars will be mentioned further in Section 1.3. A ring is often a region of increased star-

formation at approximately a constant radius from the nucleus, and can occur in the

form of inner or outer rings. Both bars and rings can occasionally be manifestations

of a recent gdaxy-galaxy interaction, and so will be further discussed in Section 1.3.

1.2.2 Active Galaxies

The radiation of AGNs is primarily non-thermal in nature, which means it cannot be

explained solely by stellar processes, including supernovae. Since much of the total

luminosity in active galaxies comes from their nuclei they are referred-to as active

galactic nuclei (AGN); these nuclei can be more luminous than the galaxy itself.

Table 1.1 presents some sample order-of-magnitude luminosities of various objects.

There are several classes of AGNs, ranging from QSOs to radio galaxies, Blazars,

Seyferts, and LINERs (Low Ionization Nuclear Emission-line Region galaxies). QSOs

are very luminous compact objects found at relatively high redshifts (large distances)

and were originally observed to be very point-like, similarly to a star (hence the

name: Quasi Stellar Object, or QSO for short). Radio galaxies and Blazars (a name

coined for both BL Lac objects and Optically Violently Variable Quasars (OWs))

are another type of active galaxy found predominantly as elliptical galaxies. Radio

galaxies are perhaps not quite as luminous as QSOs, but they can have very radio-

Ioud nuclei and often large radio lobes found well outside the optical galaxy which

are fueled by jets of material emanating fiom the nucleus. Seyfert galaxies have

moderate lurninosities for AGNs but have spatial densities - 10* times greater than

QSOs making them much easier to study in detail. Seyfert galaxies are found almost

exclusively as spiral galaxies. At the low-Iuminosity end of the activity class are

LINERs which have occasionaliy been cdled mini-Seyferts (Robson l996), since they

also occur primarily within spiral galaxies.

Table 1.1: Luminosities of various objects

Object Total LuminosiS. Sun 1 La 1 0 ~ ~ W typical galaxy 10'' La 1 0 ~ ~ W LINER S I O ~ O L ~ 1oJ6w Se yfert 10" La 1oJ7 W QSO ~ 1 0 ~ ~ ~ ~ 1 0 ~ ~ ~

1.2.2.1 Active Galactic Nuclei

A question that cornes to mind then is, "where is this extra luminosity coming from

in AGN?" or "what powers an active galaxy?". In general AGNs show some or al1 of

the following properties:

1. Very high luminosity from an unresolved nucleus.

2. Non-thermal radiation which cannot be explained solely by stellar processes.

3. Significant variability on relatively short time-scales of days to weeks, indicating

that the emission is originating from a region smaller than a light-week.

4. High ionization emission lines from material moving a t high velocities within

this small region.

5. Jets, lobes, and other explosive material being emitted bom this region (found

only in some AGNs);

The current leading theory to explain the power source of AGNs involves the accretion

of gas onto a supermassive black hole (SBH) at their galactic centers. The mas of

such an object is estimated to be 107-9 Mg, and so the SBH has a Schwarzschild

radius of 0.1 - 10 AU. This SBH is fed by a surrounding accretion disk, and in order

to support the luminosity of an active galaxy, the SBH must sustain an accretion rate

of approximately 0.1 - 1 Ma yr-'. A key problem in AGN research involves the origin

of this gaseous material and how it fuels the accretion disk, as well as determining

the length of t h e for which such activity lasts.

In summary, there are several classes of active galaxies, al1 of which are powered

by an accreting supermassive black hole. 1 wil l now focus on one class of active galaxy:

Seyfert galaxies.

1.3 Seyfert Galaxies

Seyfert galaxies are a class of active galâxy discovered by Car1 Seyfert in the 1940s.

Galaxies which exhibited broad emission lines were selected for his study (emission

lines are absent in normal galaxies). These galaxies are also predominantly spiral

galaxies, and contain a very bright and star-like core (Seyfert 1943; Seyfert 1947).

1.3.1 Properties and Types

As mentioned earlier, Seyfert galaxies are a separate class of AGN with moderate

luminosity, appearing almost exclusively as spiral galaxies. They are noted for an

unusually bright nucleus which appears star-like, as well as containing high-ionization

emission lines (this is not the case for normal galaxies). Optical spectra of a Seyfert

galaxy contain permitted emission Iines from hydrogen as well as He 1, He11 (neutral

and singly ionized helium), and Feu; there is also the presence of forbidden lines from

species such as [O 11, [O II], [O ml, [N U] , [S II], [Fe W] , and [Fe X] . Based on their optical spectra, Seyfert galaxies are classified a s Type 1 or Type

2. Figure 1.4 shows some sample spectra for both types of Seyferts in their observed

hunes with their major features labeled. The Seyfert 1 spectrum is presented in the

top panel (NGC 7469), and the Seyfert 2 spectrum is in the middle panel (NGC 1388).

In both cases, the lower curve represents the entire spectrum, while the upper curve is

Sample Seyfert Spectra I ~ ~ " I . " ' I ' ' ' ' . ~ ' ' . - l

HB [O In1 NCC 7469 :

Figure 1.4: Sample spectra of Type 1 and 2 Seyfert galaxies and a normal galaxy

an expanded view to enhance the lower-intensity features. The bottom panel displays

a normal galaxy (M32) for cornparison. In this panel the lower curve is the galaxy's

spectrum and the upper curve is the spectrum with a smooth continuum Ievel divided

out. These differences will be discussed further in Sections 1.3.1.1 and 1.3.1.2.

1.3.1.1 Seyfert 1

Type 1 Seyferts are characterized by having very broad permitted lines, with velociw

widths in the range 1,000- 10,000 kms-'. The forbidden lines are narrower, with

velocities '1,000 kms-l. The broad lines are believed to corne from a region of the

AGN which is located 51 pc from the SBH. The narrow lines are thought to originate

in a region surrounding the central "engine" at a distance of 10-100 pc.

In Type 2 Seyferts, both the permitted lines and the forbidden lines have similar

widths, corresponding to velocities 51,000 km s-l. I t is thought in this case that

both lines originate in the region of the AGN, 10 - 100 pc distant fiom the SBH

(depending on the intrinsic luminosity of the source).

1.3.1.3 Fractional Types

There are also subclasses of Seyfert galaxies based on their spectra. The categories

now recognized are types 1, 1.5, 1.8, 1.9, and 2. Type 1.5's are galaxies in which the

permitted lines contain both a broad component and a narrow component. Types

1.8 and 1.9 have mainly namow permitted lines with a weaker broad component in

the H a and H 4 lines. For the remainder of this thesis, 1 will refer to Seyfert 1s as

consisting of types 1 and 1.5, and Seyfert 2s as consisting of types 1.8, 1.9, and 2.

1.3.2 Unified Model

In the past decade the so-called Unified Model has emerged which attempts to descnbe

both broad-lined and narrow-lined AGN using a single model. Figure 1.5 shows

the Unified-Model view of a hypothetical AGN at various scales, which 1 will now

describe. (This Figure was adapted from Robson (1996), which was in turn adapted

from Blandford, Netzer, and Woltjer 1990). At the very center of the AGN (IO-* pc

or 20 AU) is a rotating SBH, which is surrounded by a thin, radiating accretion disk.

The accretion-disk region is surrounded by fast-moving broad-line emission clouds

(called the Broad-Line Region (BLR)), which extend from 10-3 pc out to 1 pc. The

"pcI massiveHll* / formation regions

m 'rnoi8cuiar and dust

Figure 1.5: An illustration of AGN at various scales

BLR has typical velocity widths of 5000 kms-l, as mentioned earlier. Closest to the

SBH, the BLR is ionized by the central radiation, producing High-Ionization Line

(HIL) clouds, which change into a Low-Ionization Line (LIL) region that is radiated

by the extended accretion disk a t the 0.1 pc scale. Moving outwards to 100 pc, we find

that the BLR is surrounded by a toms of molecular gas and "low7' velocity narrow-Iine

clouds (called the Narrow-Line Region (NLR)), with a typical velocity of 500 km s-'.

The molecular toms is an o b s c u ~ g cloud of material which can effectively hide the

AGN core and BLR from sight under certain viewing angles. Beyond the molecular

toms at the 1 kpc distance scale is a disk of molecular gas and dust which contains

massive H star-formation regions. These star-formation regions may be "fed" by a

bar just outside this zone.

According to the Unified theories, the main distinction between Seyfert 1s and 2s

arises from the viewing angle (i.e. the inclination of the toms to the line of sight),

and depends on the opening angle created by the molecular toms (Figure 1.6 contains

a schematic representation of this). In Seyfert ls, the line-of-sight is perpendicular

to the torus and thus the BLR can be seen; but in Seyfert 2s, the molecular torus

obscures the BLR, so only the NLR is visible (Osterbrock 1989; Osterbrock 1993;

Kukula et al. 1994; Robson 1996; Antonucci 1993). Lending support to the Unified

theory is the observation that some Seyfert 2s can appear to possess a BLR (type

1 spectra) when observed in polarized light (Antonucci and Miller 1985); the BLR

emission is reflected (and thus polarized) by material between the NLR clouds. With

the Hubble Space Telescope (HST), it is hoped that images of the molecular torus in

nearby AGNs will be acquired (Ward 1996), lending hrther support to the Unified

Model.

Figure 1.6: Se jer t orientation

10

1.3.3 Int eraction/Merger Hypot hesis

As noted in Section 1.2.2.1, fueling the AGN "monstery7 presents one of the greatest

outstanding challenges to extragalactic astronomy. As seen in the Unified Model, gas

falling into the SBH radiates gravitational potential energy, producing the required

luminosity. What must be addressed is the mechanism by which the fuel is brought

to the central region. An attractive theory which explains this involves gas losing

angular momentum within a non-axisymmetric gravitational potential (Barnes and

Hernquist lggl), though the question still remains of where this gas cornes from. The

"interaction/merger hypothesis" indicates that either directly (Bekki and Noguchi

1994) or indirectly (Barnes and Hernquist lggl), initiation of activity is caused by

a perturbation by an interaction or merger with a companion galaxy. In the direct

case, an actual merger may take place, in which material is transfered or tidally

stripped from a companion object; this method would be required for a host without

a sufficient gas supply of its own. In the indirect case, it is sufEcient to simply perturb

the host galaxy so that its own supply of gas will initiate activity. Bars in galaxies

are an efficient way of transporting gas to central regions, md these can be produced

fiom a perturbing interaction. In either case, the current theory suggests that the

triggering of Seyfert activity is caused by galaxy-galaxy interactions involving two

galaxies of cornpaxable m a s . This would suggest that the environment of Seyfert

galaxies should be richer than the environment of the control sample.

There have been a e e t y of studies that have examined the triggering mechanism

in AGNs. The theoretical groundwork was established by Toomre and Toomre (1972)

and an environmental relation was k t suggested by Adams (1977) using observa-

tional evidence for the case of Seyfert galaxies. Since this pioneering work, there have

been a nurnber of analyses in more recent times that continue to probe this ques-

tion. For example, Nesci (1986) examined the fiequency of Seyfert galaxies in gdaxy

clusters and determioed that they are found in open to medium clusters but not in

compact clusters, and similarly that they are more commonly found in the outskirts

of the cluster rather than the inner regions. McLeod and Ftieke (1995) investigated

the frequency of bars and rings in Seyfert galaxies in order to study the triggering

mechanism. AGN trîggering has also been examined by observing the orbital and

kinematic clues of Seyfert galaxies and their cornpanions by Keel (1996).

1.3.4 Objective

This thesis will attempt to test the interaction hypothesis. To accomplish this, the

environments of Seyfert galaxies and a control set of normal galaxies wil l be examined

for recent interactions or perturbations. This environmental examination involves

searching for cornpanion galaxies around the hosts and light asymmetries of the hosts

whicb may be indicative of a recent interaction.

1.4 Thesis Objective

The nearby environments of Seyfert galaxies as well as a control sample of normal

galaxies will be examined in order to test the interaction hypothesis. Many studies

have been undertaken to address this question, though most of these were based on

the Palomar Observatory Sky Survey (POSS), which possesses inherent problems for

analysis. To accomplish this, and avoid the problems with the POSS, CCD data

were acquired for a sample of 32 Seyfert galaxies and a control sample of 49 normal . galaxies. In order to minimize possible selection effects, the two sample sets have

been well matched in redshift, luminosity, and morphological type. This thesis will

accomplish two tasks: determine whether the control sample can in fact be fairIy

compared with the Seyfert sample and then examine and compare the environrnents

of the two sarnples in order to test the interaction model. Testing the interaction

model with these data involves a variety of tasks: finding optical companion galaxies

to the host galaxies, examining the hosts' surface-brightness profiles as well as their

ellipticity and posit ion-angle profiles, and detennining the frequency of morphological

features such as bars, rings, and tidal tails. Before describing these analysis techniques

in detail (Chapter 2), 1 will discuss previous studies which have attempted to test the

interaction model.

1.4.1 Previous Work

Several others have compared Seyfert galaxies and non-active galaxies and studied

their environments. These studies often involve determining the frequency of corn-

panion galaxies around the host galaxies.

Dahari (1984,1985) used the POSS to examine the frequency of companion galax-

ies around Seyfert galaxies using a sample of 93 Seyfert galaxies and a control sample

of 279 galaxies. The selection of his control sample was without regard to morpho-

logical type or redshift, but was based on large galaxies that were nearby on the same

POSS plate. Dahari used galaxy counts £rom Shane (1975) to account for contam-

ination by background galaxies and thus statistically derive the number of physical

companions. Using this technique, he detected a significant excess of close physical

cornpanions around Seyfert galaxies compared to his control sample.

Fuentes-Williams and Stocke (1988) (FWS) also undertook a similar analysis using

the POSS but chose a control sample that matched the morphology and lurninosity of

the Seyfert sample. They measured and counted the number of companion galaxies

within a specified angular distance of each of the 53 Seyfert galaxies and 30 control

galaxies. They determined that there is only a marginal excess of bright companions

around Seyfert gal;urie~, but that there is an excess of faint companions (though not

as large as the excess found by Dahari).

Rafanelli, Violato, and BmEolo (1995) repeated Dahari's type of analysis using

99 Seyfert 1 and 98 Seyfert 2 galaxies and a control sample of 197 galaxies. Their

control sample was chosen by using a spiral galaxy near each Seyfert. Their findings

were similar to Dahari's in that the Seyfert galaxies had a statistical excess of physical

companions.

.4 detailed and extensive study using the POSS was undertaken by Laurikainen

and Salo (1995). Their sample consisted of 104 Seyfert galaxies and 138 control galax-

ies. They paid careful attention to the selection of the control sample and attempted

to understand the biases that would be introduced depending on the selection cri-

teria. They repeated Dahaxi-type tests and FWStype tests with their data, and in

both cases found an excess of companions around Seyfert galaxies. However, their

own analysis revealed only a marginal excess of companions which were concentrated

around the Seyfert 2s, implying that Seyfert 1s and 2s are in dinerent environments.

Other similar surveys have been performed by MacKenty (1989, 1990) and Keel

et al. (1985) for example, who find an excess of companions around Seyfert galaxies.

As noted above, there are a few who do not find an excess of companions, and so no

consensus has yet been reached regarding the interaction hypothesis as it relates to

Seyfert galaxies.

Chapter 2

Observations and Reduct ion

Techniques

2.1 Introduction

This chapter will describe the acquisition of the data, as well as the reduction, pro-

cessing, and analysis techniques that were used to extract information about the

galaxies. This discussion is split into three parts. Section 2.2 wiIl discuss the acqui-

sition of the data. Section 2.3 will descnbe the preprocessing of the images. The

anaiysis techniques used to andyze the data are described in Section 2.4.

2.2 Observations

images were obtained of the Seyfert galaxies and the control galaxies in the Johnson

Bband and R-band using the 0.9-m telescope at Kitt Peak National Observatory

(KPNO). The telescope consists of a 0.9 meter primary mirror with a focal ratio of

fl7.5. The data were taken on May 16-24, 1991 UT by M.M. DeRobertis and were

transfered to 8mm Exabyte tapes for transport and analysis.

2.2.1 Selection of Seyfert Galaxies and Control Galaxies

For this survey, 32 Seyfert galaxies and a sample of 49 control galaxies were chosen.

AU galaxies were selected from the Center for Astrophysics (CfA) Redshift Survey

(Huchra and Burg 1992), which is spectroscopically complete to magnitude 14.5 in

the appropriate sky regions. Laurikainen et al. (1994) note that biases which are

not easily understood could be introduced into the andysis if the Seyfert sample

and the control sample are not well matched in redshift, morphological type, and

luminosity. To minimize the selection effects of our data, for each Seyfert galaxy one

or two control galaxies were selected from the CfA survey and were well matched to

the Seyfert in terms of redshift, morphology, and absolute magnitude. By minirnizing

the differences between the two sarnples, it was hoped that a meaningful cornparison

of their environments would be possible.

2.2.2 Charge-Coupled Devices

A charge-coupled device (CCD) was used for acquiring the data. A CCD is a photo-

electric device that is made of silicon (or other similar semiconducting material) and

is divided into a 2-dimensional m a y of pixels. When a photon is absorbed in a pixel,

an electron is fieed and accumulates in a potential well created by an applied voltage

on the &ont side of the chip during the exposure. An image is fomed by collecting the

electrons stored in each pixel at read-out. CCDs typically contain millions of square

pixels. Each pixel subtends a solid angle on the sky which depends on the optics of

the telescope. One of the most important aspects of CCDs is that their response to

light is linear (i.e. 1 photon tt 1 electron), with Quantum Efficiencies (QE) typically

- 50 - 90% over visible wavelengths.

CCDs are not perfect detectors. The data can be conected for some of the inherent

imperfections, however. In the read-out process, noise is introduced while rneasuring

the total charge in each pixel (this is called "read-noise"). Also added to the data is

the b i s , which is the instantaneous DC level of the chip's electronics, as well as the

dark current which arises from the thermal noise (although because these detectors

are cryogenically cooled, the dark current is insignificant). There are also pixel-to-

pixel QE variations across the chip which need to be corrected for, as well as tnMa.1

light variations caused by the opening and closing of the shutter. CCDs also have

"cosmetic'' defects (blocked columns) as well as "hot" pixels (which accumulate an

excess charge) and "cold" pixels (which have a charge deficit). One of the most

important limitations of CCDs is their limited dynamic range which can lead to

saturated pixels (which can subsequently lead to ''bleedinq" of charge along columns

below the saturated pixels). This limitation arises fiom the fact that most CCDs

use a 15-bit Analog-to-Digital Converter (ADC), resulting in a dynamic range of

215 2: 32,000 Analog-to-Digital Units (-4DU). The translation of electrons into digital

units is controlled by the "gain" of the chip, and so the NI-well capacity of the

detector is typically of order IO5 e-. Thus an object brighter than this will result in

saturation and bleeding (this is why care is taken in determining exposure times for

observations).

2.2.3 Data Acquisition

Our data were acquired with a Tek2048 CCD. This device has a read-noise level of

13e- and a gain of 8.2e-/ADU. The size of the chip is 2048x2048 pixels2, but

the unvignetted portion is 1700x2048 pixels2, with a pixel size of 27pm; the image

scale at the Cassegrain focus is 0.77arcsec/pixel, yielding a field of view of 21x26

arcmin2. The detector is coated with Metachrome-2 to improve its blue sensitivity.

See Figure 2.1 for a plot of the sensitivity of the detector as a function of wavelength

Tek2048 DQE and B and R Filter Transmission , O0 I l 1 f i ) ' ' 1 ' . ' I l ' ' . 1 - I \ i' -

- f \ .

- -

wavelength (nm)

Figure 2.1: Detector Quantum Efficiency (DQE) plot for Tek2048

(solid cuwe) .

The exposures relevant to this work were taken through the Johnson R-band filter,

which is a "red" filter peaked at 700 nm with a full-width-half-max (FWHM) of 210

nm. Sorne images were also taken in B-band, a "blue" filter peaked at 420 nm with

FWHM of 90 nrn. Figure 2.1 shows the relative transmission curves of the R and B

filters (dotted and long-dashed curves respectively).

2.3 Preliminary Reduction

Much of the preliminary reduction of the data was performed by K. Hayhoe and

M.M. DeRobertis. The preprocessing, photometric calibration using standard stars,

and measurernent of the apparent magnitudes of the host galaxies were cornpleted

using a combination of Image Reduction and Analysis Facility (IRAF) and Picture

Processing Package (PPP) developed by Yee (1991).

2.3.1 CCD Pre-Processing in IRAF

CCD images require a certain amount of manipulation to correct for the detector's

imperfections. Shese include removing the DC level of the exposure (bias fkames),

dark current due to thermal noise (dark frames), and high and low spatial frequency

QE variations (flat frames). The bias level is determined by averaging a series of

zero-second exposures. Dark current is accounted for by appropriately scaling a long

exposure taken wit h the shutter closed. Pixel-to-pixel and large-scale QE variations

across the chip can be removed with a flat field, which is a high-signal exposure of a

uniformly illuminated reflective screen or the twilight sky (both of which were used

in these reductions) .

Taking these into account, the data were processed in the following manner. Each

raw image was overscan-corrected by using a 5th order polynomial fit to the overscan

region, thereby removing the DC level. An overscan region is a series of .V 20 extra

columns which are read out after the image buffer has been flushed, and thus contain

the instantaneous DC level for that exposure. The actual bias images showed no 2-

dimensional structure (they were flat) and so it was not necessary to subtract the bias

fiames. Based on a series of dark images taken throughout the night, the dark current

was negligible for the relevant exposure tirnes, and so was ignored. A series of dome

flats and sky Bats were also taken periodically during the o b s e ~ n g run. These dome

flats were averaged together and illumination-corrected using the sky flats. Quantum

efficiency variations were corrected by dividing the data by the resulting flat-fields.

This procedure is also described by DeRobertis, Hayhoe, and Yee (1997), and can be

summed up in the following equation:

Raw Image - DC level Final Image =

Flat (dome, sky) - DC level

Since this thesis deals with the nearby environrnents of the program objects, the

images ivere typically cropped to a size of 512x512 pixel2 (or larger if necessary),

with the host galaxy in the center of the frame. DeRobertis, Hayhoe, and Yee (1997),

paper 1. and DeRobertis, Yee, and Hayhoe (1997), paper II, utilized the uncropped

images in order to study the large-scale environrnents of the galaxies.

2.3.2 P hotometric Cdibration

Once the program images have been pre-processed, they c m be calibrated. This in-

volves determining the transformation coefficients so that raw intensity counts can

be converted to apparent magnitude or energy units as if the objects were observed

above the atmosphere. The calibration was accomplished using Landolt (1992) stan-

dard stars. Images of 10 - 15 of these stars were taken throughout each night. The

transformation coefficients were t hen calculated fi-om the standard stars' instrumental

magnitude using IR4F7s phot cal routines, with a calibration error of I0.07 magni-

tudes. Once these constants are known, magnitudes of any object in the images can

be computed.

The instrumental magnitude, r , is defined in Equation 2.2, where f is the flux in

counts, and t is the exposure time in seconds. The instrumental magnitude r is then

transformed into an apparent magnitude R via Equation 2.3, where 5 is the zero-point

correction, k'X is the airmass term (kt is the extinction coefficient) due to the fact

that as the object gets closer to the horizon (Le. a i r m a s , X, increases), its light

suffers more atmospheric attenuation, and E ( B - R) is the colour term accounting for

wavelengt h-dependent scattering caused by the atrnosphere. Upon calibration, it was

found that nights 1-6 had approximately the same solutions, while nights 7 and 8 had

a different solution. The computed transformation coefficients are given in Table 2.1.

The (B - R) colour was taken as a nominal +l.50 based on the average galaxy colour

derived fiom the limited number of B and R images.

Table 2.1: Apparent magnitude transformation coefficients Nights < k' 45 (B - R)

(mag) (mag/X) (ma4 1-6 20.38 -0.116 0.016 t l . a o 7-8 20.42 -0.132 0.079 t1.50

2.3.3 Host-Galaxy Magnitudes

Once the transformation coefficients have been computed, the apparent magnitudes

of the host galaxies may be measured. This step was accomplished with PPP using

circular apertures and an appropriately sized sky-background annulus. The galau-'s

magnitude converged to a couple of hundredths of a magnitude within these apertures.

Light from foreground stars was subtracted fiom the galaxy 's integrated magnitude

if the star was within the galaxy's aperture, and the magnitudes were corrected for

Galactic absorption (as provided by the NASA/IPAC Extragalactic Database (XED),

where AR = 0.55 A B ) .

2.4 Image Analysis

This section Nil1 describe the various methods used to analyze the data in order to

determine the structural parameters of the host galaxies and to study their nearby en-

vironments. To accomplish t his: image statistics were first acquired (Section 3 -4.1).

after which the light distributions of the host galaxies were fitted using elliptical

isophotes (Section 2-42) which were then fitted to standard galaxy models (Sec-

tion 3.1.3). Cornpanion objects were then searched for (Section 2-44) and unusual

morphologies of the hosts noted (Section 2-45). Finally, various parameters and

statistics were cornputed based on this analysis in order to compare the two samples

(Section 2.4.6).

2.4.1 ImageStatisticsandEditing

Image statistics provide very important parameters for analysis and reduct ion. These

are measured using IRAF7s irnexamine. The mean background sky level and noise

(standard deviation of the background level) were computed by measuring counts

in roughly 10 5x3 boxes a t blank areas on the image. The mean value was then

subtracted from the image using imarith. The term seezng in astronomy is a rneasure

of the image quality and refers to the apparent disk produced by turbulence in the

Earth's atmosphere when observing a point source (such as a star). This disk is

usually modeled by a Gaussian with a characteristic FWHM for al1 point sources on

any given exposure (the exact shape is called the Point Spread Function (PSF)). The

seeing was determined by measuring the FWHM of several bright, unsaturated stars

on each image. The seeing varied between 1.4-3.0 arcseconds, with an average of

2.05 & 0.42 arcseconds. The centroid of each host g a l q was aIso computed by using

the centering routines in imexamine. Finally a- stars, ion events. blocked columns.

or satellite tracks that contaminated the host galaxy were replaced by a 4th order

interpolated background using imedit (See Appendku A.1.3 for details of this task).

2 A.2 Elliptical Isophotal Analysis

At this point we wish to calculate the surface-brightness profile, elliptici% and posi-

tion angle of the major axis of each host galaxy. Surface brightness is a measure of

intensity per unit area in an extended object and is often written in terms of mag-

nitudes per square arcsecond. Ellipticity is defined as E = 1 - b/a, where a is the

semi-major axis length and b is the semi-minor axis length. Position angle is the di-

rection in which the major axis points, and is measured from North through East. To

accomplish this, IR4F2s STSDAS/Ellipse task was used, which fits elliptical isophotes

to the galôuy. This task returns a data file containing the following parameters as

a function of the semi-major axis length: Intensity (in counts per pixel), ellipticity.

position angle (orientation of the major-axis), ellipse center, ellipse harmonics (de-

scribed below), number of iterations, stop code (reporting any problems during the

computation), and al1 pertinent fonnal uncertainties.

The E l l i p s e task is an important part of the andysis and thus its algorithm

wiil be discussed in some detail. Jedrzejewski (1987) described a variation of this

algorithm in determining surface photometry of elliptical galaxies. Depanures from

a pure ellipse can be described by a series of coefficients to an orthogonal set of

harmonic functions of the form:

where R are the intensity-contour points, and p is the azimuthal angle. The first two

orders of harrnonics (A1, BI ,A2: 82) indicate errors in the fitted ellipse. whereas the

third and fourth-order t e m s indicate an "egg-shaped" , "heart-shaped" , or "bo's;

shaped" ellipse. The way this is implemented in the algorithm is that the intensity of

the galaxy is sarnpled around the ellipse a t equal intervals of the eccentric anomal- E

at a specific semi-major radius. The following equation is then fitted by a weighted

least-squares routine to solve for the harrnonic coefficients and constant term:

The ellipticity r and the position angle 6 of the ellipse are then adjusted to make the

fit better (NB: ellipse centers were held fixed in our analysis) via:

where

That is, Ir is the derivative of the intensity in the direction of the major âuis ewl-

uated a t the semi-major length a(). This least squares and correction procedure is

implemented iteratively until a sufficiently good fit is made (i.e. I ( E ) = constant).

-4 minimum of 15 iterations are made, up to a maximum of 100. -4t this stage. the

third and fourth-order harmonics are calculated via least squares kom:

a t which point al1 parameters for that semi-major radius are written to a file. The

error-bars in intensity are obtained fiom IRAF by computing the rrns scatter of

intensity dong the fitted ellipse. The length of the semi-major axis is then increased

by 10% and the whole procedure is repeated. This continues until the specified

maximum radius is reached; the procedure is then repeated from the initial radius

until the minimum radius.

One potentiai problem that could arise fiom this algorithm arises from its inter-

polation scheme. For the inner 20 pixels, the algorithm uses a bilinear interpolation

algorithm which can produce ellipticities that are systematicdly too low in the 3-10

pixel range. This arises from the nature of the interpolation introducing its own

cos(2p) term (i.e. 84. This effect is most severe for galaxies that are Battened

near the center; hoivever, this is generally not a problem because seeing distorts the

isophotal contours in the core in any case (as noted earlier, the seeing varied between

1.8 - 3.9 arcseconds).

For each host galaxy, the ellipse task was executed twice. In the first run. the

centroid, a, and 0 were allowed to Vary in order to confim the centroid position found

by imexanine. The results from the second run (in which we held the center fked)

were used in the subsequent analysis. Most galaxies were analyzed using e l l i p s e

with a minimum semi-major radius set to 1.8 pixels (using a srnaller value results

in numencal problems, and the inner few pixels give physically unrealistic results

anyway). -4 few galaxies were fit using a third mode of e l l i p s e , in which their

centers were was held fured, E = O and t? = O" (i.e. circular apertures). when the

second run had extreme difficulty in fitting ellipses.

In some cases, the host galaxy is very close to a large companion galaxy. When

this occurs. the two galaxies need to be deblended via the following process. which is

illustrated using NGC 5541. Figure 2.2 shows the original image of both host and

companion galaxies (al1 four panels use the same contour levels for visual uniformity).

The first step involved isolating the companion galaxy by rotating the image 180"

around the host galaxy's center and subtracting this from the original image 1 (cal1

this new image BI . Figure 2.3 shows NGC 5541 with the rotated host subtracted out).

Figure 2.2: Sample deblending of Figure 2.3: Sample deblending of NGC 5541: original image I NGC 5541 with cornpanion isolated, im-

age B1

Figure 2.4: Sample deblending of NGC 5541 with host isolated, image Al

Figure 2.5: Sample deblending NGC 5541 with clean host? image .A2

Ell ipse would then be run on the companion galaxy in image B1, and a model galaxy

B V would be constmcted using the task bmodel (an IR4F routine which constructs

an image based on results fiom ellipse). Mode1 Byod is then subtracted from the

original image I resulting in image Al, thus isolating the host galaxy (Figure 2.4

shows the first-order isolated host galaxy of NGC 5541). Similarly, a model galaq-

AY*~ is constmcted by running ellipse and bmodel on the host ga1a.q- in image

=Il, which can then be subtracted fiom I to produce yt another image with the

companion isolated. This process is performed iteratively until a clean profile of the

isolated host is acquired (Figure 2.5 shows the clean image of NGC 5541).

2.4.3 Surface Brightness Profile Fitting

Now that the azimuthally averaged intensity as a function of the length of the semi-

major avis has been measured for each host galaxy, the surface-brightness profile can

be fitted to standard g a l q models (which were discussed in Section 1.2.1). We first

used a three-cornponent mode1 consisting of an exponential disk (Freernan 1970). an

T ~ / ~ bulge (de Vaucouleurs 1948), and a central Gaussian point source to model the

star-like nuclei of the Seyferts. in linear units, the intensity f at any given radius r

may then be expressed as:

which can be converted to surface brightness (mag/arcsec2) via the transformation

(cf. Equation 2.3):

p ( r ) = -2.5 log (m) + f + k'X + r (B - R) t A

where .A is the area subtended by each pixel (0.77 arc~ec /px)~ . The fitting is restricted

to these three standard models for consistency even though galasies can be much

more cornplex (e.g.. bars, rings, holes in disks, etc. Such features, however, require

even more parameters to determine. There are also alternative functional forms for

the bulge, though the de Vaucouleurs profile is appropriate since Seyfert galaxies are

mostly "early-type" spirals with large bulges). The data are fit to Equation 2.10 using

a chi-squared hypersurface minimization routine (Press et al. 1992). ln t his program

the relative f lues fd, fb, and fN, and the scale radii ro and r, are solved for, while a

is held constant since it is related to the seeing; by definition a = 0.42466 FW'HM.

See Appendix -4.2.1 for more details on this program. As soon as the function's

chi-squared reaches a global minimum, the paramet ers, t heir formal errors. and the

reduced chi-squared are returned.

An alternative fitting method was also used for the Seyfert sample. This method

involved fitting a two-component disk and bulge beginning 5 pixels from the center

where the PSF is d o m to 5 2 % peak intensity for the median seeing. The quantity fx

is then computed by subtracting the extrapolated two-component fit from the data

and interpreting the excess flux as being contributed by the PSF (see Appendix A.2.1

for more details). The issues of uniqueness of solutions and numerical stabilit- can

be addressed by comparing the results of the first and second methods.

Other studies have also been accomplished by examining the surface-brightness

profiles of Seyfert galaxies. Alonso-Herrero, Ward, and Kotilainen (1996) and Koti-

lainen, Ward, and Williger (1993) for instance used a similar three-component. chi-

squared minimization fitting routine. McLeod and Rieke (1995) on the other hand

used an alternative technique in analyzing the surface brightness profiles by first

performing PSF subtraction followed by a two-component fit.

2.4.4 Cornpanion Galaxy Searching

At this point, we searched for optical companions to the hosts on the cropped images.

As we approached this problem from a statistical viewpoint, we were not searching for

physical companions, but merely for optical companions. Thus our lack of redshift or

distance information for such galaxies is not problematic. The search for extra galaxies

rvas performed by careful visual inspection using SAOimage with the assistance of

IR4F's imexamine. -211 candidate objects were analyzed using the radial profile t 001.

and based on their FWHM and E , were classified each as a star or g a l ~ v . Objects in

which the FWHM was less than the seeing were interpreted to be ion events; objects

with a FWHM sufficiently greater than the seeing were interpreted as galaxies. and

those Mth FWHM similar to the seeing were classified as stars (unless E indicated

ot herwise) .

The integrated intensity for al1 objects classified as galaxies was measured using an

aperture of radius i pixels from within the radial-profile tool. If the galaxy was large.

the aperture radius was increased appropriately to accommodate it. The centroid

and flux of each galaxy were recorded so that the projected distances and magnitudes

could be calculated later. Since a meaningful qualitative cornparison is desired, we

Mposed a projected cut-off metric radius of 200 kpc (using Ho = 50 h km s - ' ~ p c - ' ) :

this way we are searching for companions to a common, similar radius in the rest

frame of the host galaxies.

2.4.5 Unsharp Masking and Morphology

We then looked at the general morphology and "interaction level" of al1 the hosts.

This consisted of a two-phase visual inspection of the hosts to look for things such as:

amorphous or unresolved features, spiral arms, bars, rings, distortions. faint disturbed

companions, bridges, tails, and jets. Phase one involved visual inspection of the s -

subtracted images. Phase two involved visual inspection of unsharp-masked images.

Such images were created by taking the non-sky-subtracted images and convolving

them Mth a flux-preserving Gaussian kernel with FWHM 4 times the seeing. The orig-

inal image was then divided by the convolved image producing the "unsharp-masked"

image (alternatively. the images could have been subtracted). This unsharprnasking

Example of Unsharp-Masking/Convolution 1

x (arbitrary units)

Figure 2.6: 1-D example of unsharpmasking/convolution

technique is illustrated in one dimension in Figure 2.6. The top panel represents an

artificial original image which consists of a narrom Gaussian (representing a star), a

broad Gaussian (representing a large galaxy), and a broad Gaussian with a narrower

Gaussian superposed (representing a large galaxy with a close companion). The mid-

die panel shows the image after it has been convolved ~ 6 t h a Gaussian as described

above. The bottom panel shows the division of the two images; note that the large

galaxies nearly disappear, and that the star and companion gai- are clearly evident.

As seen from the example, unsharp-mas king eliminates the low spatial-frequencies and

enhances the high spatial-frequencies. Features such as spirals. bars. rings. and very

close companion galaxies al1 have their own unique signatures on unsharpmasked im-

ages as can be seen in the following examples. Figure 2.7 demonstrates how a bar and

ring structure appear. Figure 2.8 illustrates the appearance of spiral arms. Figure 3.9

shows the signature of a close companion and a normal bright star. Figure 2.10 also

dernonstrates a close companion object . Morphological features were noted using this

technique, and confirmed the featilres observed visually.

2 A.6 Galaxy Parameters and Statistics

Distances, magnitudes, luminosities, and gravitational tidal influences were t hen com-

puted.This was done so that Seyfert galaxies can be compared to the control galaxies.

as well as to compare Seyfert 1s and 2s. The first value computed was the distance to

the host galaxies, from which can also be derived the image scales and thus the pro-

ject ed companion-host separation distance. The distance to the hosts (as a function

of redshift) is given to a very good approximation by:

for

where D is the distance, Ho is Hubble's constant, and z is the redshift of the

galaxy. In al1 the distance calculations, we use Ho = 50 h km S - ~ M ~ C - ' , so that

c/Ho = 5996 h-' hlpc, where c is the speed of light and h is the dimensionless Hubble

constant.

The projected separation distances s can then be derived from the image scale.

and are given as: s = ,!3 D where p is the angular separation given in radians. Xow

that the distancetype parameters have been determined, the absolute magnitudes of

the hosts and companion galaxies (based on the projected distance) : can be calculated

via:

N 5289 R Unsharp N 3968 A Unsharp

Figure 2.7: Sample unsharp-masked im- Figure 2.8: Sample unsharp-masked image of NGC 5289 age of NGC 3968

N 4172 R Unsharp N 6111 A Unsharp

1 i ; j U . , U . i 1

*O b

v . I - - . , / . . Q t A

Figure 2.9: Sample unsharp-masked im- Figure 2.10: Sample unsharp-masked image of YGC 4172 age of NGC 6111

where MR is the absolute magnitude and .A@ is the extinction in our own Galaxy

(in R-band). Using the galaxies' absolute magnitudes, we can now calculate their

luminosities relative to L* (which represents the luminosity of a typical large galaxy)

which corresponds to l'LI; = -20.6 + 5 log(h) (Schechter 1976) using the same value

for Ho as this thesis. This transforms to M i = -22.1 using B - R = +l.5 as a

nominal average galaxy colour. The luminosity is then given by:

The next parameter that can be calculated is the tidal influence which the compan-

ions have on the host galaxy (based on their projected distances). Tidal force. Q, is

proportional to hl/s3 where M is mass of the perturbing object and s is the separa-

tion distance. -4ssuming that the m a s of a companion galaxy is proportional to its

luminosity (Le. constant rnass-to-light ratio MIL) , mhich is a reasonable approxi-

mation since we are concerned with the order of magnitude of the tidal parameter,

we can thus define a maximum tidal influence as:

where Li is the luminosity of companion galaxy i, and si is its separation distance

from the host. The full tidal influence on a host galaxy is then given by:

where N is the number of companion galaxies around the host. AIso calculated was

the magnitude difference between the host and cornpanions (AMR = RCmP - Rhosf).

Chapter 3

Discussion of Seyfert Galaxies

Introduction

Using the techniques outlined in Chapter 2, the reduction of the 32 Seyfert galaxies

will be discussed in this chapter. Results of the image analysis including contour maps

and surface-brightness profiles of the galaxies will be presented. Quantities derived

and computed from this analysis such as magnitudes, distances, and properties of the

galaxies will also be presented.

Analysis

This section will present images of the Seyfert galaxies, their surface-brightness pro-

files, and a brief discussion regarding the reduction of each galaxy. The images pre-

sented are displayed in t e m s of isophotal contours, where the lowest contour is at

30 above the background, and the remaining contours are a t incrernents of 0.2 mag-

nitudes (i.e. intensity ratios of 1.20) unless otherwise noted. All contour maps have

North up and East to the left. The surface-brightness profiles being presented have

been converted

are also shown.

into

The

apparent magnitudes. The mode1 components used in the fit

dotted line represents the Gaussian PSF, the short-dashed line

represents the bulge component , the long-dashed line represents the disk component .

while the solid line indicates the sum of the components; the data-points and their

error-bars are the data that were retumed from the e l l ipse task. The ellipticity pro-

files and position-angle (PA) profiles are also discussed, but appear in Appendis B.

These plots delineate 60m the ellipticity of the galaxy and the P.4 of the major avis

V a r y as a function of the semi-major axis length (in arcseconds). What follow in Sec-

tion 3.2.1 are the g a l a q contour images, surface-brightness profiles, and a description

of each galaxy in the Seyfert data set.

3.2.1 The Galaxies

Mrk 0231 This is a disturbed galaxy that contains a tidal bridge to a cornpanion

galaxy 57'' to the S. The surface-brightness profile (Figure 3.2) fits well, though

the outer envelope seems a little brighter than expected, and no Gaussian PSF was

required (perhaps due to the obvious tidal distortions). Based on the PA profile

(Figure B.3), the elliptical contours do a complete twist around from center to edge.

See Figure 3.1 for the contour map of Mrk 0231.

Mrk 0461 This galaxy appears as an ordinary spiral. Its surface-brightness profile

(Figure 3.4) fits very well (using circular apertures from el l ipse) , using only bulge

and disk components, with no need for a Gaussian PSF. The lack of a PSF is perhaps

caused by some bar-type structure). The galaxy's PA (Figure B.1) is fairly stead-

and its ellipticity varies as expected (though there is some hint of bar activity near

4"). See Figure 3.3 for Mrk 0461's contour map.

Mrk 0471 This is a spiral galaxy with a bar. No Gaussian PSF was needed (due

to the bar perhaps) in the fit to the surface-brightness profile (Figure 3.6) which fits

Calaxy profile for Mrk023I i " " i " " t " " l " " 1

16

5 10 15 20 25 Scmi-Major ans (arcseconds)

Figure 3.1: Intensity contour map of Figure 3.2: Radial profile and fit of PvIrk 0231 Mrk 0231. XE = 0.31

Figure 3.3: Intensity contour map of Mrk 0461

Galaxy profile for Mrk046 1

L " " " ' " ' " ' " ' 1

O 10 20 30 Semi-Major axis (arcseconds)

Figure 3.4: Radial profile and fit Mrk 0461. XE = 0.07

Mrk 471 R 900s CaIaxy profile for Krk0471


Figure 3.5: Intensity contour map of Figure 3.6: Radial profile and fit of Mrk 0471 Mrk 0471. X E = 0.67

well with just a disk and bulge. The P.4 undergoes a perpendicular twist just after

the bar at 10" (Figure B.2). The contour map is found in Figure 3.5.

Mrk 0789 This is a very peculiaq distorted galaxy with some odd-shaped extended

regions and an unusually shaped core (see Figure 3.7 for contour map). The object

20" to the SE is a bright star. The surface-brightness profile (Figure 3.8) is somewhat

noisy, but fits very well with al1 three components. Its PA is quite steady at about

50°, t hough its ellipticity varies across the galaxy (Figure B .4).

Mrk 0817 This galaxy appears as a normal spiral, with a close companion galaxy

11" to the S (see Figure 3.9). The surface-brightness profile fits reasonably well with

al1 three components (Figure 3.10). The ellipses were fit with the close companion

removed. The galaxy7s contours t i s t slowly throughout, though its ellipticity behaves

reasonably well (Figure B. 1).

Mrk 789 R 900s 1329:1122 Galsxy profile for Mrk0789 = r . s , ~ , ! , l ~ r ! ~ ~ -

1 - rn

\ l . - . , t \, , ,

-

-20 -10 O 1 O 20 5 10

Arcsec Semi-Major axis (arcseconds)

Figure 3.7: Intensity contour rnap of Figure 3.8: Radial profile and fit of Mrk 0789 Mrk 0789. XE = 0.11

Mrk 817 R 900s Calaxy profife for MrkOB17

2 4 6 8 10 12 Semi-Major axis (arcseconds)

Figure 3.9: Intensity contour map of Figure 3.10: Radial profile and fit Mrk 0817 Mrk 0817. XE = 0.98

Figure 3.11: Intensity contour rnap of Mrk 0841

Galary profile for Mrk0841

F " ' " " " " ' " " " " " 1

2 4 6 8 1 O Semi-Major axis (arcsecanda)

Figure 3.12: Radial profile and fit of Mrk 0841. X: = 4.02

Mrk 0841 This is a plain-looking disk galaxy with a strong Gaussian PSF. The fit

to the surface-brightness profile was poor nurnerically: t hough it appears acceptable

(Figure 3.12). The ellipticity profile shows the galaxy to be very circular (Figure B.8)

and hence the P.4 is irrelevant. The contour map of Mrk 0841 is found in Figure 3.11.

UGC 06100 This is a normal spiral galaxy; however. its surface-brightness pro-

file fits well with a strong bulge component and no Gaussian PSF (Figure 3.14).

UGC 06100's PA is very steady and its ellipticity behaves as expected (Figure B.2).

.An altematively used name for this galaxy is A1058+455, and its contour map is

found in Figure 3.13.

UGC 08621 This is a normal spiral galaxy with prominent spiral m s . Its surface-

brightness profile fits well primarily with a disk component, though a Gaussian PSF

is etident (Figure 3.16). The galaxy is roughly circular, and its PA appears to twist

around with its spiral arms (Figure B.8). This galaxy is also called 1335t39. and its

Figure 3.13: Intensity contour map of UGC 06100


Calaxy prolie for UGCOBIOO l " " i ' " ' 1 ' " 1 ' " i '

18 - I

5 10 15 20 25 Semi-Major axis (arcseconds)

Figure 3.14: Radial profile and fit UGC 06100. X: = 0.52

Calaxy prolie for UGC0862 1

18 - i " " T ' " ' i " " i " " ! "

C

. . 5 10 15 20 25

Semi-Major axis (arcseconds)

Figure 3.16: Radial profile and fit UGC 08621. X: = 0.44

contour map is found in Figure 3.15.

Figure 3.17: Intensity contour rnap of NGC 3080

Galaxy profile for NGC3080

" " ' " ' ~ ' " ' " " ' ~ "

5 10 15 20 Semi-Major axis (arcseconds)

Figure 3.18: Radial profile and fit of NGC 3080. X: = 1.17

NGC 3080 This is a normal spiral galaxy with a small, close cornpariion object

(Iikely a faint star) to the S a t 20". There is a very large companion galaxy 4.3' to

the SW (UGC 05371, an interesting galaxy in itself). An adequate fit was made to

the surface-brightness profile using al1 three components (Figure 3.18). There is a

slight twist in the isophotes a t 6", which is associated with a decrease in ellipticity

(Figure B.1). The contour map of NGC 3080 is found in Figure 3.17.

NGC 3227 This is a large spiral galaxy with an large elliptical companion galaq-

(NGC 3226) 2' m. There is evidence of dust lanes and extended material surrounding

the galaxy (possibly tidal in origin). The surface-bnghtness profile fits well, and used

al1 three components (Figure 3.20). Outside of the core, the P.4 and ellipticity are

fairly stable (Figure B.6). NGC 3227's contour rnap is in Figure 3.19.

N 3227 R (300) Calaxy profile for NCC3227

O 20 40 60 80 LOO Semi-Major axis (arcseconds)

Figure 3.19: Intensity contour map of Figure 3.20: Radial profile and fit of NGC 3227 NGC 3227. = 0.68

Figure 3.21: Intensity contour map of NGC 3362

Calaxy profile for NCC3362

l8 8

\

24 \ \

l ! . . , 1 , . . . 1 .


Figure 3.22: Radial profile and fit NGC 3362. XZ, = 0.41

NGC 3362 This is a spiral g d a q nrith bright spiral arms. The surface-brightness

profile fits well, though it consisted only of a bulge and disk (Figure 3.22). The PA

twists around over 90" with the spiral m s , while the ellipticity increases up to 0.1

and gradually becomes circular a t the edge of the galaxy (Figure B.3). See Figure 3.21

for the contour map of NGC 3362.

N 3516 FI 900s Caiaxy profile for NCC3516

-60 4 0 -20 O 20 40 60 O 10 20 30 40 50


Figure 3.23: Intensity contour rnap of Figure 3.24: Radial profile and fit of NGC 3516 NGC 3516. X: = 4.86

NGC 3516 This is an ordinary spiral galaxy with very faint spiral ams. There

are a number of close small companions, notably three at about 1' to the S, NE, and

NW (see contour map: Figure 3.23). A few foreground stars were removed from the

image prior to the isophotal analysis; however, the surface-brightness profile has a nu-

merically poor fit (Figure 3-24), but visually appears acceptable. The isophotes twist

back and forth once by about 60" (Figure B.2), with no particularly odd behaviour

in ellipticity.

N 3718 R (600) Galaxy profile for NGC3710

-100 -50 O 100 O 50 100 150


Figure 3.25: Intensity contour map of Figure 3.26: Radial profile and fit of NGC 3718 NGC 3718. X: = 0.32

NGC 3718 This is a distorted spiral galaxy with a dust lane through its center.

There is a noticeable amount of extended material in the N and S directions as well.

The surface-brightness profile fits well using a l l three components (Figure 3.26). The

P-4 twists nearly 60" at 75" (Figure %.7), as the isophotes of the central region are

almost perpendicular to those of the rest of the galaxy (Figure 3.25).

NGC 3786 This spiral galaxy has a faint ring present, as well as a large companion

galaxy (NGC 3788) 1.4' to the K. There appears to be a tidal tail to the E caused by

the interaction with NGC 3788. There is another companion galaxy 80" to the SW:

the object 2' to the SE is a star. The surface-brightness profile fits reasonabiy well

, though no Gaussian PSF was used, perhaps due to the ring and tidal distortions

(Figure 3.28, the ring structure shows some artifacts at a radius of 20"). The PA

angle is quite steady, and the ellipticity behaves predictably as in Figure B.4. The

contour map of NGC 3786 and NGC 3788 can be found in Figure 3.27.

N 3786 R 9 0 s Mfk 744 GaIaxy profide for NCC3786

Figure 3.27: Intensity contour map of Figure 3.28: Radial profile and fit of NGC 3786 NGC 3786. 2 = 0.82

N 3982 R 900s Galaxy profile for NGC3982

O 10 20 30 40 50 Semi-Major axis (arcseconds)

Figure 3.29: Intensity contour map of Figure 3.30: Radial profile and fit of NGC 3982 NGC 3982. XE = 2.99

NGC 3982 This galaxy has very pronounced spiral features. Its surface-brightness

profile fits poorly (Figure 3.30), even after removing nine data points between 10 - 20"

(some kind of ring-type feature or disk-hole). Perhaps due to the peculiar nature

of this galaxy, no Gaussian PSF was recovered. In this same region, the PA and

ellipticity behave oddly as well. as the isophotes temporarily flatten and twist around

(Figure 8.5). See Figure 3.29 for the contour map of NGC 3982.

N 4051 R 300s Gafaxy profile for NCC4051

-100 -50 O 50 100 O 50 100 150

Arcsec Serni-Major ans (arcseconds)


NGC 4051 This galaxy has very prominent spiral arms with several large clumps

in these m s . There is also a large, odd extended region in the NE, of unknown

origin. The fit to the surface-brightness profile is somewhat poor (Figure 3.321, and

no Gaussian PSF was recovered. The PA is quite steady (Figure B.7), though the

isophotes flatten quite a bit due to the inclination of the galaxy (which is i - 55').

The contour map of NGC 4051 can be found in Figure 3.31.

N 4151 R 300s Gdaxy profile for NCC4 15 1

-50 O 50 O 20 4 0 60 80



NGC 4151 This is a spiral galaxy with a bar structure and a partial ring. There

is a moderate sized spiral cornpanion (NGC 4156), 5' NE. The surface-brightness

profile fits adequately (Figure 3.34); the actual fit was executed on data acquired via

circular apertures. The PA and ellipticity are very well behaved (the inner 20" are

meaningless for the PA, since the isophotes are very nearly circular in that region as

seen in Figure B.5). NGC 4151's contour map can be found in Figure 3.33.

NGC 4235 This is a high-inclination (i = 75") spiral galaxy with noticeable dust

lanes as well as a slight asymmetry in the NE edge of the galaxy. Nearly 50 stars

were removed in the galaxy's vicinity in order to fit isophotes to the galaxy. The

resulting surface-brightness profile fits very well, though using only bulge and disk

components (Figure 3.36). The absence of the Gaussian PSF is perhaps indirectly

due to the dust lane. The PA is extremely steady, and the ellipticity also behaves

very well (Figure B.7). See Figure 3.35 for the contour rnap of NGC 4235.

N 4235 R 9005 Calaxy profile for NCC4235

O 50 100 Semi-Y ajor axis (arcseconds)

Figure 3.35: Intensity contour rnap of Figure 3.36: Radial profile and fit of NGC 4235 NGC 4235. XE = 0.47

N 4253 R 900s Galaxy profile for NCC4253



NGC 4253 This spiral galaxy contains a bar and a faint partial ring. The surface-

brightness profile fits well using al1 three components (Figure 3.38). The PA are fairly

steady until .- 18" where the bar ends and the isophotes become circular in the outer

region (Figure B.5). See Figure 3.37 for the contour map of NGC 4253.

Semi-Y ajor aris (arcseconds)

Figure 3.39: Intensity contour map of Figure 3.40: Radial profile and fit of NGC 4388 NGC 4388. XY = 0.23

NGC 4388 This is a high-inclination ( 2 = 75") spiral galaxy with very promi-

nent dust, and is located in the Virgo Cluster. Many stars were removed pnor to

isophotal andysis. The surface-brightness profile fits well with just two components

(Figure 3-40), though it appeaxs as though a Gaussian PSF would be needed if there

was higher resolution data in the core. The PA is very steady, and the isophotes

quickly become flattened, though there is a fair amount of noise in the inner 20"

(Figure B.?). The contour map of NGC 4388 can be found in Figure 3.39.


Galaxy pro l i e for NCC5252


Figure 3.42: Radial profile and fit of NGC 5252. XE = 0.18

NGC 5252 This galaxy has a somewhat pointed shape, and there are no obvious

spiral m s . The surface-brightness profile fits very well to just bulge and disk corn-

ponents (Figure 3.42). A Gaussian PSF was not recovered since the bulge fits very

well to the inner pixels. The isophotes are well behaved in terms of PA and ellipticity

(Figure B.4). The contour map of NGC 5252 is found in Figure 3.41.

NGC 5256 This galaxy is obviously a mergerlinteraction in progress, and there

are tidal tails streaming off in several directions (N, SW, SE). Due to the presence

of the two nuclei in close proximity of each other and the irregular isophotes, I was

unable to fit any elliptical isophotes to this galaxy. The contour map of NGC 5256

is found in Figure 3.43.

NGC 5273 This is a ordinary looking galaxy with no noticeable spiral ams. There

is a moderate sized spiral galaxy located 3.3' away to the SE. The fit to the surface-

brightness profile is poor, though it appears visually acceptable (Figure 3.45). The



7

0 20 40 60 80 Semi-Major m i s (arcseconds)


Figure 3.45: Radial profile and fit NGC 5273. XE = 2.39

fit was unable to recover a Gaussian PSF as the bulge appears to fit adequately

to the central region. The PA and ellipticity of the galaxy are fairly well behaved

(Figure B.8). NGC 5273's contour map is found in Figure 3.44.


Calaxy profile for NGC5283

y---?---

Semi-Major axis (arcsecoods)

Figure 3.47: Radial profile and fit of NGC 5283. XY = 0.37

NGC 5283 This object appears as a spiral galaxy with no obvious spiral arms.

There is a srnall companion object very close, 19" to the NW. The surface-bnghtness

profile fits very well using only a bulge and disk (Figure 3.47). It is unknown why a

Gaussian PSF was not recovered, though the bdge fits well to the central region of

the galaxy. The PA appears sornewhat steady (within its error-bars, which are large),

and ellipticity is well behaved (Figure B.8). The contour map of NGC 5283 is found

in Figure 3.46.

NGC 5347 This spiral galaxy contains a prominent bar and ring. There is also a

companion object (large clump in a spiral a n n ) 19" to the S. The surface-brightness

profile fits well with al1 three components (Figure 3.49). The PA is very steady and




the galaxy's ellipticity behaves as expected for a large bar (Figure BA). NGC 5347's

contour map can be found in Figure 3.48.

NGC 5548 This spiral galaxy is ringed. There also appears to be a faint outer ring

(perhaps a remnant From some polar interaction). The fit to the surface-brightness

profile is mediocre, and used only a combination of a bulge and a G a w i a n PSF

(Figure 3.51); odd that no disk component was needed. Ellipse had some trouble

calculating some parameters of the isophotes outside of 20'' (Figure B.3), but inside

this region the PA is twisting slightly while the isophotes are expanding irregularly

in several directions. See Figure 3.50 for the contour rnap of NGC 5548.

NGC 5674 This is a baned spiral galaxy with a ring. There was a certain amount

of difficulty in fitting elliptical isophotes to this galaxy (outside of 15"), as can be seen

with the PA and ellipticity profiles in Figure B.6. The fit to the surface-brightness

profile is poor, but is partly explained by the artifacts produced by the bar and ring


Gaiaxy profile for NCC5548

l6 6

O 10 20 30 40 Semi-Major axis (arcseconds)

Figure 3.51: Radial profile and fit NGC 5548. X: = 1.07

N 5674 R 900s Galmcy profile for NCC5674

O 1 O 20 30 Semi-Major axis (arcseconds)

Figure 3.52: Intensity contour map of Figure 3.53: Radial profile and fit NGC 5674 NGC 5674. X: = 2.74

(Figure 3.53). The contour map of NGC 5674 can be found in Figure 3.52.

N 5695 R 900s Cds*y profile for NCC5695

O 10 20 30 40 Semi-Major axis (srcseconds)

Figure 3.54: Intensity contour map of Figure 3.55: Radial profile and fit of NGC 5695 NGC 5695. xU = 0.87

NGC 5695 This spiral gdaxy contains a hint of a bar. The star 15" N was removed

pnor to isophotal analysis. The surface-brightness profile fits well, but only used bulge

and disk components (Figure 3.55). Perhaps the partial bar played some part in the

i n a b i l i ~ to recover a central point source. The PA is steady, and the ellipticity

behaves as expected for a baned galaxy (Figure B.5). See Figure 3.54 for the contour

map of NGC 5695.

NGC 5929 This spiral g a l q is undergoing an interaction with a close (< 3OU),

spiral galaxy (NGC 5930). The fit to the surface-brightness profile is adequate; how-

ever, there was no disk component fit to it (Figure 3.57). The PA twists around

slightly, but the ellipticity behaves appropriately (Figure B.6). The contour map of

NGC 5929 can be found in Figure 3.56; note that NGC 5930 is at the center of the

image.

N 5929 Fi 900s again Calaxy profile for NCC582B 1 ' " ' l " " ~ " " ~

50 -

% 0 a

-50 24 -

I ; . . m I . . . . ' l l . , l . -

-50 O 50 O 10 20 30 Arcçec Semi-Ysjor axis (arcseconds)


NGC 5940 This spiral galaxy contains a pronounced bar. The surface-brightness

profile fits very well, and uses all three components (Figure 3.59). The PA twists

around with the bar and spiral arms, and the ellipticity behaves as a barred galaxy

should (Figure B.6). NGC 5940's contour map can be found in Figure 3.58.

NGC 6104 This galaxy seems to be the result of two merging galaxies, currently

surrounded by some khd of ring structure. Due to the confusion caused by the

merger, no isophotes were fit to this galaxy, and thus no surface-brightness profile is

available. See Figure 3.60 for the contour map of NGC 6104.

NGC 6814 This spiral galaxy has a partial bar and partial ring. The galaxy image

was contaminated by nurnerous stars and a man-made satellite passing through, al1

of which were removed prior to isophotd analysis. The surface-brîghtness profile fits

well, though it only utilized bulge and disk components (Figure 3.62). Perhaps the

lack of a Gaussian PSF is due to either the interesting morphological features or the

N 5940 R 900s Calaxy profiic for NGC5940

5 1 0 15 20 25 Semi-Major axis (arcscconds)




t l " ~ l " ' l ' ~ ~ ' ~ " ' ~ " l


Figure 3.62: Radial profile and fit NGC 6814. X E = 0.66

image-editing process. The galaxy flattens into a partial bar at 20", and becomes

circular beyond that, though the PA twists over a very large range (Figure B.3). The

contour map of NGC 6814 can be found in Figure 3.61.

3.3 Summary of Seyfert Galaxy Properties

The following tables summarize much of the information about the individual Seyfert

galaxies. Information regarding the basic properties of the hoçt galaxies, image statis-

tics, elliptical isophotal analysis parameters, surface bnghtness profile results, and

cornpanion statistics will be presented.

Table 3.1 shows some basic properties of the Seyfert galaxies, such as their loca-

tion, magnitude, and redshift. Table 3.2 provides important image statistics for the

Seyfert data, including the seeing and the airrnass of the exposures. Table 3.3 gives

some brief details of the isophotal analysis and the parameters used in the ellipse

fitting. Table 3.4 provides the results from the three-component surface-brightness

58

profile fitting (method 1), as well as the fractional luminosity contained in each corn-

ponent. In a similar format, Table 3.5 presents the results from the two-component

surface-brightness profile fitting (method II, as outlined at the end of Section 2.4.3

and Section A.2.1), to provide a compaxison with the three-component fit so that

uniqueness of solutions can be noted. As can be seen, the disk parameters are much

more stable than the bulge parameters. A further discussion of these fits follows in

Section 5.2.2. Finally, Table 3.6 shows distance, luminosity and cornpanion galauy-

related parameters of the hosts.

Table 3.1: Basic Properties of the Seyfert galaxies in the dataset

Name a(1950.0) 6(1950.0) m~ MR z Type Mrk 0231 12~54~05?0 +57°08'38" 12.66 -24.36 0.0422 Mrk 0461 Mrk 0471 Mrk 0789 Mrk 0817 Mrk 0841 UGC 06100 UGC 08621 NGC 3080 NGC 3227 NGC 3362 NGC 3516 NGC 3718 NGC 3786 NGC 3982 NGC 4051 NGC 4151 NGC 4235 NGC 4253 NGC 4388 NGC 5252 NGC 5256 NGC 5273 NGC 5283 NGC 5347 NGC 5548 NGC 5674 NGC 5695 NGC 5929 NGC 5940 NGC 6104 NGC 6814

Column 1, name of the galaxy; columns 2-3, the Right Ascension and Dechation of they galaxy (Erom NED); column 4, the apparent magnitude of the host, as measured by M.M. DeRobertis (Paper 1); column 5, the absolute magnitude of the host; column 6, the redshift (from NED); and column 7, the Seyfert Type of the galaxy (fkorn NED).

Table 3.2: Image statistics of the SeSert galaxies

Name seeing sky skya X exptime

Mrk 0461 Mrk 0471 Mrk 0789 Mrk 0817 Mrk 0841 UGC 06100 UGC 08621 NGC 3080 NGC 3227 NGC 3362 NGC 3516 NGC 3718 NGC 3786 NGC 3982 NGC 4051 NGC 4151 NGC 4235 NGC 4253 NGC 4388 NGC 5252 NGC 5256 NGC 5273 NGC 5283 NGC 5347 NGC 5548 NGC 5674 NGC 5695 NGC 5929 NGC 5940 NGC 6104 NGC 6814

Column 1, name; column 2, seeing (this is the FWHM of the PSF); column 3, sky background level; column 4, noise in the image (which 1 refer to as "sky O"); column 5, the airmass at the time of exposure; and column 6, the exposure time.

Table 3.3: Ellipse parameters for the Seyfert galaxies

Name am= (4 (PA) (") ( 1 -b /a ) (N-E)

Mrk 0231 25 0.25 -140 Mrk 0461 Mrk 0471 Mrk 0789 Mrk 0817 Mrk 0841 UGC 06100 UGC 08621 NGC 3080 NGC 3227 NGC 3362 NGC 3516 NGC 3718 NGC 3786 XGC 3982 NGC 4051 NGC 4151 NGC 4235 NGC 4253 NGC 4388 NGC 5252 NGC 5256 NGC 5273 NGC 5283 NGC 5347 NGC 5548 NGC 5674 NGC 5695 NGC 5929 NGC 5940 NGC 6104 NGC 6814

Column 1, name; column 2, maximum semi-major axis length used in the ellipse fitting; column 3, approximate ellipticity of the galaxy near the outer edge of the profile; and column 4; approximate Position Angle of the major-axis of the galaxy near the edge.

Table 3.4: surface-brightness profile parameters for the Seyfert galaxies

Name Pb p, xY LD LB LN

Mrk 0231 Mrk 0461 Mrk 0471 Mrk 0789 Mrk 0817 Mrk 0841 UGC 06100 UGC 08621 NGC 3080 NGC 3227 NGC 3362 NGC 3516 NGC 3718 NGC 3786 NGC 3982 NGC 4051 NGC 4151 NGC 4235 NGC 4253 NGC 4388 NGC 5252 NGC 5256 NGC 5273 NGC 5283 NGC 5347 NGC 5548 NGC 5674 NGC 5695 NGC 5929 NGC 5940 NGC 6104 NGC 6814

Column 1, name; column 2, scale radius of the disk; column 3, effective radius of the bulge; column 4, central surface brightness of the disk; column 5, effective surface brightness of the bulge; column 6, central surface brightness of the Gaussian PSF; column 7, the reduced chi-squared goodness of fit of the model; columns 810, the fractional lurninosity contained in each the disk, bulge, and PSF respectively.

Table 3.5: surface-brightness profile parameters for the Seyfert galaxies, method II.

Mrk 0231 Mrk 0461 Mrk 0471 Mrk 0789 Mrk 0817 Mrk 0841 UGC 06100 UGC 08621 NGC 3080 NGC 3227 NGC 3362 NGC 3516 NGC 3718 NGC 3786 NGC 3982 NGC 4051 NGC 4151 NGC 4235 NGC 4253 NGC 4388 NGC 5252 NGC 5256 NGC 5273 NGC 5283 NGC 5347 NGC 5548 NGC 5674 NGC 5695 NGC 5929 NGC 5940 NGC 6104 NGC 6814

Column 1, name; column 2, scale radius of the disk; column 3, effective radius of the bulge; column 4, central surface brightness of the disk; column 5, effective surface brightness of the bulge; column 6, central surface brightness of the Gaussian PSF: column 7, the reduced chi-squared goodness of fit of the model; columns 8-10, the fractional luminosity contained in each the disk, bulge, and PSF respectively.

Table 3.6: Distance and luminosity parameters for the Seyfert galaxies

Name da imscale A L N Q

Mrk 0461 Mrk 0471 Mrk 0789 Mrk 0817 Mrk 0841 UGC 06100 UGC 08621 NGC 3080 NGC 3227 NGC 3362 NGC 3516 NGC 3718 NGC 3786 NGC 3982 NGC 4051 NGC 4151 NGC 4235 NGC 4253 NGC 4388 NGC 5252 NGC 5256 NGC 5273 NGC 5283 NGC 5347 NGC 5548 NGC 5674 NGC 5695 NGC 5929 NGC 5940 NGC 6104 NGC 6814

Column 1, name; column 2, distance, based on angular distance derived from the galaxy's redshift; column 3, image scale, based on projected distance at the distance of the host galaxy; column 4, R-band Galactic extinction (fiom NED); column 5, absolute R luminosity; column 6, number of optical companion galaxies found; and column 7, cumulative tidal effect of the companion galaxies upon the host.

Chapter 4

Discussion of Control Galaxies

4.1 Introduction

Using the techniques outlined in Chapter 2, the reduction of the 49 control galaxies

will be discussed in this chapter. Results of the image analysis including contour maps

and surface-brightness profiles of the galaxies will be presented. Quantities derived

and cornputed from this analysis such as magnitudes, distances, and properties of the

galaxies will also be presented.

4.2 Analysis

This section will present images of the control galaxies, their surface-brightness pro-

files, and a brief discussion regazding the reduction of each galaxy. The presentation

of this data is in the same format and style as in Chapter 3, and similarly includes a

discussion about morphology, surface-brightness profile goodness of fit, and isophotal

behaviour What follows in Section 4.2.1, are the galaxy contour images, surface-

brightness profiles, and a description of each galaxy in the Seyfert data set.

4.2.1 The Galaxies

1031 +5307 R 900s Calary profile lor UCC05734

4 0 -20 O 20 40 O 1 O 20 30 40

Arcsec Semi-Major kxis (arcseconds)

Figure 4.1: Intensity contour map of Figure 4.2: Radial profile and fit of UGC 05734 UGC 05734. = 0.58

UGC 05734 This spiral galaxy has a hint of a bar. There are several small close

cornpanion galaxies. The surface-brightness profile fits well, though it could be im-

proved with better data (Figure 4.2). The PA is very steady, and the ellipticity also

behaves well (Figure B.20). An alternatively used name of this galaxy is 1031+5307.

See Figure 4.1 for the contour rnap of UGC 05734.

UGC 07064 This spiral contains both a bar and a ring. The fit to the surface-

brightness profile is poor, even after removing six data points from the ring (Fig-

ure 4.4). The PA twists slightly with the bar in the inner 10" (Figure B.12). UGC 07064's

alternative name is 1202+3127. The contour map of UGC 07064 is found in Figure 4.3.

UGC 09295 This spiral galaxy is very plain iooking. The fit to the surface-

brightness profile is poor, which contains some unusual fluctuations, and consists

of only a disk cornponent (Figure 4.6). The PA is very steady, and the ellipticity be-

haves as expected (Figure B. l l ) . An alternative name for UGC 09295 is 1426+7010.

1 20243 1 27 fl 900s GaIaxy profiie for UCC07064

5 1 O 15 20 25 Scmi-Uajor exis (arcseconds)

Figure 4.3: Intensity contour map of Figure 4.4: Radid profile and fit of UGC 07064 UGC 07064. X: = 2.12

Galaxy profiie for UCCOQ295

P

5 10 15 Semi-Uajar axis (arcseconds)

Figure 4.5: Intensity contour map of Figure 4.6: Radial profile and fit of UGC 09295 UGC 09295. = 3.17

UGC 09295's contour map is found in Figure 4.5.


O 10 20 30 40 50 Semi-Major axit (arcseconds)

Figure 4.8: Radial profile and fit of UGC 10097. X: = 2.74

UGC 10097 This is a normal looking spiral galaxy, with a close small cornpanion

galaxy 40" to the N. The fit to the surface-brightness profile is numerically poor,

though it visually appears very acceptable (Figure 4.8). The PA twists very slightly

throughout the galaxy, and the ellipticity appears well behaved (Figure B.12). An

alternative name for this galaxy is 1554+480. The contour map of UGC 10097 is


UGC 10407 This galaxy is undergoing a merger or interaction, there is evidence

of about three nuclei, and the resulting gdaxy is very asymrnetrically shaped. As

a result, no isophotal analysis was performed on this galaxy, and thus no surface-

brightness profile is available; however, its contour map can be seen in Figure 4.9.

This galaxy is also called 1626+420.



Galaxy profiic for UCC11865

8

t . ~ \

5 10 15 Scmi-Major axis (arcseconds)

Figure 4.11: Radial profile and fit of UGC 11865. x2 = 0.11

UGC 11865 This spiral galaxy has a peculiar, asymmetnc shape. There are a

couple of small, very close cornpanions within 10" of the host, though the object 18"

to the NW is a foreground star. The surface-brightness profile fits very well, with a

dominant disk component (Figure 4-11). The PA and ellipticity vary somewhat across

the galaxy, following the asymmetries of the isophotes (Figure B.21). An alternative

name of this galaxy 2156+1148; its contour map can be found in Figure 4.10.

1 875 R 900s Cslaxy profile for IC875

O 1 O 20 30 40 Scmi-Major axis (arcsecoads)

Figure 4.12: Intensity contour rnap of Figure 4.13: Radial profile and fit of IC 875 IC 875. 2 = 0.75

IC 875 This galaxy is a very ordinary looking galaxy. There is a small cornpanion

30" away to the SW. The surface-brightness profile fits well as can be seen in Fig-

ure 4.13. The PA is very steady and the ellipticity behaves very well (Figure B.9).

IC 875's contour map can be found in Figure 4.12.

IC 1141 This is a normal spiral galaxy. The surface-brightness profile fits well

(Figure 4.15); the star to the SW was removed before the fit was performed. The

11141 Fi 900s Galaxy profile for ICI 141

Figure 4.14: Intensity contour map of Figure 4.15: Radial profile and fit of IC 1141 IC 1141. X: = 0.85

PA profile is steady, and the ellipticity behaves reasonably well (Figure B.11). The

contour map of IC 1141 can be seen in Figure 4.14.

NGC 3169 This is a spiral galaxy with prominent dust lanes, and a very large

companion galaxy(NGC 3166) 7.5' away (60 kpc projected distance) to the W. There

are extended regions of the galaxy which may be tidally induced by NGC 3166. The

fit to the surface-brightness profile is relatively poor (Figure 4-17), though it could

be partly explained by perturbations from NGC 3166. The PA iç very steady, though

the ellipticity takes a n unusual dip a t 30" (Figure B.ll). NGC 3169's contour map

can be seen in Figure 4.16.

NGC 3492 This is a merging/interacting galaxy with two nuclei present, as well

as a very close cornpanion galaxy (12" SW, 12 kpc projected distance). The SW

companion was deblended from the host prior to analysis, and the isophotal analysis

was performed using a minimum radius outside of the double nuclei (starting at 5").


Calaxy profite for NGC3169

F " " " " " " " " " 1

Scmi-Major axis (arcseconds)


Calaxy profile for NGC34QS

19

5 10 15 Semi-Major axis (arcscconds)


The surface-brightness profile fits very well with just a bulge cornponent (Figure 4-19),

though a sole disk component would fit reasonably wel1 also. The PA twists slightly

in this range, and the ellipticity behaves well (Figure B.9). The contour map of

NGC 3492 can be found in Figure 4.18.


-100 -50 O 50 100 O 20 4 0 80 00 100



NGC 3756 This is a relatively normal spiral galacxy. There are some isophotal

irregularities a t 40". The fit to the surface-brightness profile is poor, caused by some of

the isophotal asymmetries (Figure 4.21). The PA is mostly steady, and the ellipticity

behaves well (Figure B.16). See Figure 4.20 for the contour map of NGC 3756.

NGC 3825 This spiral galaxy contains a prominent bar. The fit to the surface-

brightness profile is numefically very poor (Figure 4.23), even after removing 5 data

points caused by the bar at 10"; however, the fit appears visually acceptable. The

PA twists nearly 180" as the isophotes follow the bar and the spiral arms, and the

ellipticity fluctuates following the same features (Figure B.17). The contour map of

Cslaxy profile for NCC3825

~ ~ ~ ~ ~ " ~ ' ~ " ~ ~ ~ " ~ ~ " " " ~

O 10 20 30 40 50 Scmi-Major axis (arcaeconds)



NGC 3825 is found in Figure 4.22; please note the the contour levels are at 0.10

magnitude increments.

NGC 3938 This galaxy has bright, clumpy spiral armç, with many small close

cornpanions (most likely large spiral clumps or H II regions). The fit to the surface-

brightness profile is mediocre (Figure 4.25). The PA fluctuates al1 over the place, and

the ellipticity behaves somewhat oddly as well (Figure B.12). NGC 3938's contour

map can be found in Figure 4.24.

NGC 3968 This spiral gdaxy contains a bar. The fit to the surface-brightness

profile is numencally poor, though acceptable visually (Figure 4.27). The PA under-

goes a very rapid perpendicular twist where the bar ends a t 20" (Figure B.17). See

Figure 4.26 for NGC 3968's contour map.

N 3938 R 900s Calkxy profile for NCC3938

O 20 40 60 BO LOO Semi-Major mis (arcseconds)







O



Figure 4.29: Radial profile and fit of NGC 4045. X: = 2.67

NGC 4045 This spiral galaxy contains a partial bar and an extended envelope.

There is a close cornpanion galaxy to the S at 1.5'. Numerically, the surface-bnghtness

profüe fits poorly, though it is visually acceptable (Figure 4.29). The PA twist around

several times, and the ellipticity varies drastically at the same location (Figure B. 13).

The contour rnap of NGC 4045 can be found in Figure 4.28.

NGC 4048 This spiral galaxy contains an object that looks like a warped bar.

There are two close cornpanions about 30" away to the SE and NIV. Due to the pres-

ence of this warped bar, the fit to the surface-brightness profile is poor, and consists

of only a disk component (Figure 4.31). The PA rernains steady throughout the bar,

and the ellipticity behaves reasonably well (Figure B.19). NGC 4048's contour rnap

is found in Figure 4.30.

NGC 4088 This spiral galaxy has a bar, and an extended feature to the NE. The

noise is very bad in this image, and as a consequence, the surface-brightness profile fits

Calaxy ptofïie for NGC4048 1 " " ~ " " " " ' " " " 1

Semi-Yajor axis (arcseconds)


N 4088 R 900s Galaxy profile for NCC4088 i " ' i r " i " ' ~ ' " ~ ~ ~ l ~

100

= l a - -

50

O

U: 2 0 < -

-50

-1 00 2 2 , l . . , 1 . . . 1 . . . 1 . 0 . l . n n-.

-100 -50 O 50 100 O 20 40 80 80

Arcsec Semi-Major axis (arcreconds)


well numericdly, but the resulting parameters are somewhat unredistic (Figure 4.33).

The PA twists somewhat in the inner 20", after which the PA and ellipticity data be-

corne bad (Figure B.18). The contour map of NGC 4088 can be found in Figure 4.32,

please note that the contour leveis are a t 0.5 magnitude increments.

N 41 72 Fi 900s Galaxy profile for NCC4 172

-40 -20 O 20 40 O 10 20 30 Arcsec Semi-Major ans (areseconds)


NGC 4172 This appears to be a normal spiral galaxy with a very close companion

15" to the S; the object 30" to the S is a star. The fit to the surface-brightness profile

is somewhat poor, being too bnght at the outer edges (Figure 4.35). The PA is v e l

steady and the ellipticity behaves well, though it flattens a t 20" due to the companion

(Figure B.lO). See Figure 4.34 for the contour map of NGC 4172.

NGC 4224 This spiral galaxy has a prominent dust lane. The surface-brightness

profile fits well (Figure 4.37, the kink in the profile a t 7" is caused by poor fitting of

the elliptical isophotes due to the dust lane cutting through that region). The PA is

N 4224 R 900s Galaxy profiie for NGC4224



very steady, and the ellipticity behaves reasonably well (Figure B.17). NGC 4224's

contour map can be found in Figure 4.36.

NGC 4352 This is a seemingly normal galaxy, with no apparent cornpanions any-

where near it. The fit to the surface-brightness profile is very poor, but appears

mediocre except a t the galaxy edge (Figure 4.39). The PA is very steady and the

ellipticity also behaves very well (Figure B.14). The contour rnap of NGC 4352 can

be found in Figure 4.38.

NGC 4375 This is a spiral galaxy with a very faint ring. The fit to the surface-

brightness profile is numerically poor, though it appears acceptable (Figure 4.41, the

bump in the profile a t 10" is likely caused by the faint ring). The PA twists by 50'

just past the ring, though the ellipticity behaves reasonably well (Figure B.10). See

Figure 4.40 for the contour map of NGC 4375.

Galaxy profile for NCC4352

' T r ' ' ' " ' " ' l

Senti-Major axis (arcseconds)

Figure 4.38: Intensity contour map of Figure 4.39: Radial profle and fit of NGC 4352 NGC 4352. X: = 10.45


4 0 -20 O 20 40 O 10 20 30 Arcsec Semi-Major axis (arcaeconds)



Calaxy profile for NCC4477 t ~ " ' " " " " ' 1


Figure 4.43: Radial profile and fit of NGC 4477. = 8.42

NGC 4477 This is a barred spiral galaxy with a large cornpanion 5.3' to the SE. The

surface-bnghtness profile fits very poorly numerically, using only a bulge component,

though the fit is visually acceptable (Figure 4.43). The PA twists 60' after the bar,

and the ellipticity behaves as expected for a bar (Figure B.10). The contour map of


NGC 4799 This is a normal spiral galaxy. The objects 14" E and 50" SE are stars.

The surface-brightness profile fits well (Figure 4.45). The PA is very steady, and the

ellipticity behaves very well (Figure B.18). See Figure 4.44 for the contour map of

NGC 4799.

NGC 4944 This is a normal spiral galaxy, though not much more c m be said

because of the high level of noise in the image. The fit to the surface-brightness

profile is mediocre (Figure 4.47). The PA is very steady, and the ellipticity is very

wetl behaved (Figure B.18). NGC 4944's contour map can be found in Figure 4.46.



9


Figure 4.45: Radial profile and fit NGC 4799. = 0.84




Cniaxy profide for NCC4954

F " " " ' " " ' " i ' ~

O 1 O 20 30 Semi-Major axis (armeconds)


NGC 4954 This is a spiral galaxy with a couple of nearby, fair-sized companions.

The surface-brightness profile fits adequately (Figure 4.49). The PA is fairly steady,

and the ellipticity behaves well (Figure B.15). The contour map of NGC 4954 can be


NGC 5289 This spiral galaxy contains a bar and a ring, with a very close small

companion 14" (3 kpc projected distance) to the SW. The fit to the surface-brightness

profile is very poor, though it can be partly explained by the presence of the bar and

ring (Figure 4.51). The PA is very steady, but the ellipticity takes an odd dip at 20"

(Figure B.18). See Figure 4.50 for the contour map of NGC 5289.

NGC 5375 This is a spiral galaxy containing a bar (which has clumps on the ends).

The fit to the surface-brightness profile is nurnerically poor, but visually acceptable

(Figure 4.53). The PA twists slightly within the bar, and the ellipticity indicates the

presence of the bar also (Figure B.16). NGC 5375's contour map can be found in


I6 6

O 20 40 60 Semi-Major axis (arcscconds)

Figure 4.50: Intensity contour map of Figure 4.51: Radial profile and fit NGC 5289 NGC 5289. = 5.02

N 5375 R 900s 2nd time Calaxy profile for NCC5375


Figure 4.52: Intensity contour map of Figure 4.53: Radial profile a d fit of NGC 5375 NGC 5375. XZ = 2.17

Figure 4.52.


l8 8

Figure 4.54: Intensity contour map of Figure 4.55: Radial proNe and fit of NGC 5505 NGC 5505. XE = 1.96

NGC 5505 This spiral galaxy contains a prominent bar. The surface-brightness

profile fits poorly, but is partly explainable by the presence of the bar (Figure 4.55).

The PA twists slightly throughout the galaxy, and the ellipticity behaves as expected

(Figure B.19). The contour map of NGC 5505 can be found in Figure 4.54.

NGC 5515 This galaxy is a spiral with a very faint ring. The star 23" to the

MN was removed pnor to isophotal analysis. The surfacebrightneçs profile fits well

(Figure 4.57). The PA is very steady, and the ellipticity is well behaved (Figure B.14).

See Figure 4.56 for the contour rnap of NGC 5515.

NGC 5541 This spiral galaxy is undergoing an interaction with a very close corn-

panion galaxy 15" NE. The bright star 23" to the S was removed before any isophotal

Galaxy profiIe for NCC5515

5

O 1 O 20 30 40 Semi-Major axis (arcseconds)

Figure 4.56: Intensity contour rnap of Figure 4.57: Radial profile and fit of NGC 5515 NGC 5515. X: = 0.47

Calaxy profile for NCC554 I I ' " ' l ' " ' l " " t ' " ' ~ ' "

18 - -

a - V1 6

t I

l > . * t l n n 4 * l ~ ~ . m

-20 O 20 5 10 15 20 25 Arcsec Semi-Major axis (arcseconds)


analysis. The fit to the surface-brightness profde is somewhat poor, perhaps explain-

able due to the interaction perturbing the system (Figure 4.59). The PA is relatively

steady, and the ellipticity behaves well, though there is a dip at 6" (Figure B.16).

NGC 5541's contour map can be found in Figure 4.58.


Cataxy profile for NCC5603

P " " l " " ' " " l " " ' l


NGC 5603 This is a plain looking galaxy with a couple of large, distant compan-

ions. The fit to the surface-brightness profile is poor, though it appears acceptable

(Figure 4.61). The PA is fairly steady, and the ellipticity is well behaved (Figure B.21).

The contour map of NGC 5603 is found in Figure 4.60.

NGC 5644 This is another plain looking galaxy with distant large companions.

The objects 22" NE and 38" E are foreground stars. The surface-brightness profile fit

is numerically very poor, but is visually very acceptable (Figure 4.63). The PA and

ellipticity are both quite steady (Figure B.21). See Figure 4.62 for the contour rnap

of NGC 5644.


Calaxy profile for NGC5644 L l ' r ' ' ~ ~ ' ' ' ~ " " ~ ' ' ~ ' ~ " " ~ " ~

O 10 20 30 40 50 Scmi-Major exis (arcseconds)


NGC 5690 This is a spiral gdaxy with dust and a lot of spiral clumps. There

were several contaminating stars that were removed before analysis, a s well as an

E W diffraction spike fIom a particularly bnght star. The surface-brightness profile

fits well, partly due to the noise level though (Figure 4.65). The PA is very steady,

and the ellipticity is fairly steady as well (Figure B.19) indicating an inclination of

i x 70". NGC 5690's contour map c m be seen in Figure 4.64.

NGC 5772 This is a normal spiral galaxy with no interesting features. The surface-

brightness profile fits very poorly numerically, though it appears quite acceptable

(Figure 4.67). The PA is very steady, and the ellipticity behaves well (Figure B.15).


NGC 5806 This is a spiral gdaxy with a hint of a bar; there are two very close

cornpanion objects within 1'. The fit to the surface-brightness profile is very poor nu-

merically, but it appears visualiy acceptable (Figure 4.69). The PA is very steady, but




L " " " " " " " ' " " 4


Figure 4.65: Radial profile and fit NGC 5690. 3 = 0.47

Galaxy profile for NCCS172

l " T ' " ' " ' [ I



Calaxy profile for NGC5806

t " ' ~ i " ' ~ " ~ i ~ ~ T " " i


Figure 4.69: Radial profile and fit of NGC 5806. XY = 7.42

the ellipticity shows some amount of fluctuation throughout the galaxy (Figure B.14).

See Figure 4.68 for the contour map of NGC 5806.

NGC 5876 This spiral galaxy contains a bar and a ring. The fit to the surface-

brightness profile is numencally very poor, though it appeaxs acceptable (Figure 4.71).

The PA undergoes a moderate twist at 15" following the bar. The ellipticity also

takes a jump at the same location due to the bar (Figure B.15). The contour map of


NGC 5908 This spiral galaxy is nearly edge-on (275") and contains a prominent

dust lane. The surface-brightness profile fits very well (Figure 4.73). The PA is very

steady, and the ellipticity behaves as expected for an edge-on galaxy (Figure B.19).

NGC 5908's contour map c m be found in Figure 4.72.

N 5876 R IOOOs CaIaxy profile for NCC5876

O 20 40 60 Semi-Major aris (arcseconds)


N 5908 R 900ç Calaxy profile for NCC5Q08

O 20 40 60 80 Semi-Major a*is (arcseconds)


N 5957 R 900s Cslaxy profile for NCC5957

-60 4 0 -20 O 20 40 60 O 20 40 80

Arcsec Semi-Major axis (srcseconds)


NGC 5957 This is a spiral galaxy with a bar and ring. The fit to the surface-

brightness profile is mediocre, partially due to the ring and bar (Figure 4.75). The

PA is fairly steady, though the ellipticity steadily increases until the end of the bar

where the ring starts (Figure B.17). See Figure 4.74 for the contour map of NGC 5957.

NGC 5980 This is a normal spiral galaxy with a s m d , close cornpanion 32" to

the SE. The surface-brightness profile fits adequately (Figure 4.77). The PA is very

steady, and the ellipticity is very well behaved (Figure B.15). The contour map of


NGC 6001 This spiral galaxy contains a partial bar and prominent arms. The

surface-brightness profile fits well (Figure 4.79). The PA undergoes a 90" twist dur-

ing the transition fkom bar to disk, and the ellipticity demonstrates this as well

(Figure B. 13). NGC 6001's contour map can be found in Figure 4.78.

Galaxy prolie for NCC5980 l ~ ~ " ' l ~ ~ ~ ' l " ~ ' t " " ~ ~ ~ ~ ' ~

O 1 O 20 30 40 50 Semi-Yajor sxis (arcseconds)


Calaxy profile for NCC6OOl


Scmi-Major axis (arcseconds)

Figure 4.79: Radial profile and fit NGC 6001. X E = 0.95

N 6014 R 900s Calaxy profile for NCC60 14

-40 -20 O 20 40 O 10 20 30 40 50

Arcsec Semi-Major alas (arcsccancls)

Figure 4.80: Intensity contour rnap of Figure 4.81: Radial profile and fit of NGC 6014 NGC 6014. 2 = 1.93

NGC 6014 This spiral galaxy has a bar and a partial ring. The objects 35" to

the N are stars and were removed pnor to isophotal analysis. The fit to the surface-

brightness profile is mediocre, though it appeam very acceptable (Figure 4.81). The

PA twists from the bar to the rest of the gala= and the ellipticity follows this trend

as well (Figure B.10). See Figure 4.80 for the contour map of NGC 6014.

NGC 6030 This is a normal looking galaxy. The fit to the surface-brightness profile

is poor numencally (due to small error-bars), though it is acceptable viçually (Fig-

ure 4.83). The PA is very steady, and the ellipticity behaves very well (Figure B.11).


NGC 6085 This is a normal spiral galaxy that is in a rich environment, but there

are no noticeable close cornpanion objects. The fit to the surface-bnghtness profile

is very poor; however, it appem visually acceptable (Figure 4.85). There is a slight

twist in the PA at 12", and there is an odd dip in the ellipticity at the same location

N 6030 R 900s Caiaxy profiIe for NCC8030


Figure 4.82: Intensity contour map of Figure 4.83: Radial profile and fit NGC 6030 NGC 6030. XE = 4.92

N6085R900~ Galaxy profile for NCC6085

4 0 -20 O 20 A r e c

O 10 20 30 40 Semi-Yajor axis (arcseconds)

Figure 4.84: Intensity contour map of Figure 4.85: Radial profile and fit NGC 6085 NGC 6085. XY = 6.80

(Figure B.13). NGC 6085's contour map can be found in Figure 4.84.

4 0 -20 O 20 40 O 10 20 30



NGC 6111 This is a fairly normal spiral galaxy which has a very close companion

object 13" (4 kpc projected distance) to the S. The surface-brightness profde fits

very well (Figure 4.87). The PA is very steady, and the ellipticity is reasonably well

behaved (Figure B.14). See Figure 4.86 for the contour map of NGC 6111.

NGC 6126 This is a normal spiral galaxy with a very close srnall companion object

19" (17 kpc projected distance) to the NW. The surface-brightness profile fits well, as

can be seen in Figure 4.89. Since the ellipticity indicates a very round isophotes, the

PA does not provide much information (Figure B.21). The contour map of NGC 6126

cm be found in Figure 4.88.


Calaxy proZiie for NCC6126

, " ' ' ' ' ' ' ' ~ ' ' ' ' 1 ' " " 1



N 6143 R 900s Calaxy profiie for NCC6143

O 10 20 30 Semi-Major kxis (arcsecoads)


NGC 6143 This is a spiral gdaxy with clurnpy spiral m s and a close companion

30" to the NW; the object 23" to the SE is a foregound star. The fit to the surface-

brightness profile is poor, partly explained by the bump in the profile caused by the

spiral a n n clumps (Figure 4.91). The PA twists around slightly and erratically, and

the ellipticity behaves in a similar manner (Figure B.16). NGC 6143's contour map

can be seen in Figure 4.90.

N 6155 R 900s Galaxy profile for NGC6155

-40 -20 O 20 40 O 10 20 30 40

~ C S B C Semi-Major axis (arcseconds)


NGC 6155 This spiral galaxy contains a bar, and there is a small companion object

30" (8 kpc projected distance) away to the W . The surface-brightness profile fits well

(Figure 4.93). The PA twists 50' due to the presence of the bar, and the ellipticity

is somewhat steady but noisy (Figure B.9). See Figure 4.92 for the contour map of

NGC 6155.

NGC 6196 This is a normal looking (perhaps elliptical) galaxy; there are a couple

of nearby companion objects within 1.5'. The fit to the surface-brightness profile

99

N 6196 R lOûû~ Galaxy profiie for NGC6197


O IO 20 30 40 50 Serni-Major axis (arcseconcis)


is numerically poor (due to the small enor-bars), though it is visually acceptable

(Figure 4.95). The PA is very steady, and the ellipticity behaves well (Figure B.9).

the contour map of NGC 6196 can be found in Figure 4.94.

NGC 6764 This spiral galaxy contains a bar, and there is a fair-sized companion

less than 3' away, as well as a close, small companion 25" (6 kpc projected distance) to

the N. Many foreground stars were removed prior to isophotal analysis. The surface-

brightness profile fits well, as can be seen in Figure 4.97. The PA is very steady, and

the ellipticity is well behaved (Figure B.20). NGC 6764's contour map c m be seen

in Figure 4.96.

4.3 Summary of Control Galaxy Properties

The following tables summarize much of the information about the individual con-

trol galaxies. Information regarding the basic properties of the host galaxies, image


Calaxy proNe for NCC8764

6

Semi-Yajor axis (arcseconds)


statistics, elliptical isophot al analysis parameters, surface brightness profile results,

and companion statistics will be presented.

Table 4.1 shows some basic properties of the control sample galaxies, such as their

location, magnitude, and redshift. Table 4.2 provides important image statistics for

the control data, including the seeing and the a i m a s of the exposures. Table 4.3

gives some brief details of the isophotal analysis and the parameters used in the ellipse

fitting. Table 4.4 provides the results from the three-component surface-brightness

profile fitting, as well as the fractional luminosity contained in each component. Fi-

nally, Table 4.5 shows distance. lurninosity and companion galaxy-related parameters

of the hosts.

Table 4.1: Basic properties of the control galaxies in the dataset

Name ~~(1950.0) 6(1950.0) m~ MR z UGC 05734 10~31~0893 t53°07'47f' 12.65 -23.02 0.0237 UGC 07064 UGC 09295 UGC 10097 UGC 10407 UGC 11865 IC 875 IC 1141 NGC 3169 NGC 3492 NGC 3756 NGC 3825 NGC 3938 NGC 3968 NGC 4045 NGC 4048 NGC 4088 NGC 4172 NGC 4224 NGC 4352 NGC 4375 NGC 4477 NGC 4799 NGC 4944 NGC 4954

Column 1, name; columns 2-3, the Right Ascension and Declination of they galaxy (from NED); column 4, the apparent magnitude of the host, as measured by M.M. DeRobertis (Paper 1); column 5' the absolute magnitude of the host; column 6, the redshift (frorn NED).

Table 4.1: continued

Name (r(1950.0) 6(1950.0) m~ MR z NGC 5289 13h43m01fl +41°45'11" 12.30 -21.18 0.0084 NGC 5375 13~54~4026 -I-29O24'26" 12.08 -21.27 0.0079 NGC 5505 1 4 ~ 10m06?6 +13O32'19" 13.19 -21.41 0.0142 NGC 5615 1 4 ~ 10rn34f2 +3g032'38" 12.98 -22.84 0.0254 NGC 5541 l d h 14~28% +39O49'12" 12.87 -22.97 0.0257 NGC 5603 14h21m00f9 +40°36'15" 12.86 -22.33 0.0188 NGC 5644 1.1h3Bm00?5 +12°08'58'' 11.65 -24.17 0.0254 NGC 5690 14h35m09?3 +02°30'14" 11.79 -20.96 0.0058 NGC 5772 14h49m44?1 +40°48'14" 12.22 -22.72 0.0165 NGC 5806 14~57~28!4 +02°05t20" 11.16 -21.07 0.0045 NGC 5876 1 ~ ~ 0 8 ~ 0 7 s 4 +54°41t48ff 12.16 -21.94 0.01 12 NGC 5908 15h15m23?0 +55O35'37" 11.42 -22.64 0.0110 NGC 5957 15h33m01s0 +12O12'46" 12.00 -20.85 0.0061 NGC 5980 15h39m1156 +15O56'58" 12.26 -22.28 0.0136 NGC 6001 15h45m3950 +28°46'00'' 13.21 -23.20 0.0332 NGC 6014 1 ~ ~ 5 3 ~ 2 9 s 4 +06°04'40" 12.62 -20.86 0.0081 NGC 6030 15h59m36?5 +18°05'56" 11.80 -22.94 0.0150 NGC 6085 16h10m35!0 +29O29'31" 13.09 -23.37 0.0340 NGC 6111 16~13~5295 +62031f41" 13.22 -20.59 0.0098 NGC 6126 16h19rn38?9 +36°29'37t' 13.33 -23.00 0.0326 NGC 6143 16~20*35?7 +55°12'11" 13.17 -21.87 0.0175 NGC 6155 16h24m43s6 +4B028'41" 12.37 -21.03 0.0081 NGC 6196 16~36~05% +36O 10'16" 12.33 -23.94 0.0314 NGC 6764 19h07m01?2 +50°51'08" 11.76 -21.72 0.0079

Table 4.2: Image statistics of the control galaxies

Name seeing sky skyo X exptime

("1 (-) arcsec* (ADU) ( 4 UGC 05734 2.34 & 0.04 19.55 11.2 UGC 07064 UGC 09295 UGC 10097 UGC 10407 UGC 11865 IC 875 IC 1141 NGC 3169 NGC 3492 NGC 3756 NGC 3825 NGC 3938 NGC 3968 NGC 4045 NGC 4048 NGC 4088 NGC 4172 NGC 4224 NGC 4352 NGC 4375 NGC 4477 NGC 4799 NGC 4944 NGC 4954

Column 1, name; column 2, seeing (this is the FWHM of the PSF); column 3, sky background level; column 4, noise in the image ("sky on); column 5, the airmass at the time of exposure; and column 6, the exposure time.


Name seeing sky s k y o X exptime ("1 ( ) arcsec2 (ADU) (4

NGC 5289 1.84 * 0.08 20.71 6.5 1.04 900 NGC 5375 NGC 5505 NGC 5515 NGC 5541 NGC 5603 NGC 5644 NGC 5690 NGC 5772 NGC 5806 NGC 5876 NGC 5908 NGC 5957 NGC 5980 NGC 6001 NGC 6014 NGC 6030 NGC 6085 NGC 6111 NGC 6126 NGC 6143 NGC 6155 NGC 6196 NGC 6764

Table 4.3: Ellipse parameters for the control galaxies

UGC 07064 UGC 09295 L'GC 10091 UGC 10407 UGC 11865 I C 8'75 IC 1141 NGC 3169 NGC 3492 XGC 3756 3GC 3825 NGC 3938 NGC 3968 NGC 4045 NGC 4048 NGC 4088 NGC 4172 NGC 4224 NGC 4352 NGC 4375 NGC 4477 NGC 4799 NGC 4944 NGC 4954

(") (1-b/a) (N-E) UGC 05734 0.6 155

Column 1, name; column 2, maximum semi-major axis length used in the ellipse fitting; column 3, approximate ellipticity of the galaxy near the outer edge of the profile; and column 4, approximate Position Angle of the major-axis of the galaxy near the edge.


Name %L= (4 (PA) (") ( 1 - b / a ) (N-E)

NGC 5289 NGC 5375 NGC 5505 NGC 5515 NGC 5541 NGC 5603 NGC 5644 NGC 5690 NGC 5772 NGC 5806 NGC 5876 NGC 5908 NGC 5957 NGC 5980 NGC 6001 NGC 6014 NGC 6030 NGC 6085 NGC 6111 NGC 6126 NGC 6143 NGC 6155 NGC 6196 NGC 6764

Table 4.4: surface-brightness profile parameters for the control galaxies

Name r O Te Pd P b LD LB (kpc) (kpc) (rnag/arcsec2) % ) (%)

UGC05734 1.7 38.3 17.16 23.79 0.58 37 63 UGC 07064 UGC 09295 UGC 10097 UGC 10407 UGC 11865 IC 875 IC 1141 NGC 3169 NGC 3492 NGC 3736 NGC 3825 NGC 3938 NGC 3968 NGC 4045 NGC 4048 NGC 4088 NGC 4172 NGC 4224 NGC 4352 NGC 4375 NGC 4477 NGC 4799 NGC 4944 NGC 4954

c o l u n 1, name; column 2, scale radius of the disk; column 3, effective radius of the bulge; colurnn 4, central surface brightness of the disk; column 5, effective surface brightness of the bulge; column 6, the reduced chi-squared goodness of fit of the model; and columns 7-8): the fractional luminosity contained in each of the disk and bulge respectively.


Name r O T e P d Pb LD LB (kpc) (kpc) (mag/arcsec2) (%) (%)

NGC 5289 - 4.4 - 21.01 5.02 O0 100 NGC 5375 9.4 10.0 NGC 5505 2.7 0.1 NGC 5515 3.8 13.7 NGC 5541 5.5 0.4 NGC5603 1.1 4.5 NGC 5644 15.5 7.0 NGC 5690 4.1 0.5 NGC 5772 10.4 3.2 NGC 5806 3.7 1.8 NGC 5876 16.4 4.0 NGC 5908 4.6 7.9 NGC 5957 3.7 2.9 NGC 5980 3.9 27.0 NGC 6001 9.3 0.5 NGC 6014 2.9 0.9 NGC 6030 2.4 8.2 NGC 6085 - 12.9 NGC 6111 1.7 7.1 NGC 6126 16.4 7.4 NGC 6143 5.6 6.0 NGC 6155 2.7 1.6 NGC 6196 - 10.4 NGC 6764 13.0 0.7 20.46 19.02 0.53

Table 4.5: Distance and luminosity parameters for the control galaxies

UGC 07064 UGC 09295 UGC 10097 UGC 10407 UGC 11865 IC 875 IC 1141 NGC 3169 NGC 3492 NGC 3756 NGC 3825 NGC 3938 NGC 3968 NGC 4045 NGC 4048 NGC 4088 NGC 4172 NGC 4224 NGC 4352 NGC 4375 NGC 4477 NGC 4799 NGC 4944 NGC 4954

Column 1, narne; column 2, distance, based on angular distance denved from the galaxy's redshift; column 3, image scale, based on projected distance at the distance of the host galaxy; column 4, R-band Galactic extinction (from NED); column 5, absolute R luminosity; column 6, number of optical companion galaxies found; and column 7, cumulative tidal effect of the companion galaxies upon the host.


Name dB imscale Agd L N Q ( M P ~ ) (kpc/") (mad (L*) ( L * / M ~ C ~ )

NGC 5289 SO 0.240 0.00 0.43 10 2.51 x 104 NGC 5375 NGC 5505 NGC 5515 NGC 5541 NGC 5603 NGC 5644 NGC 5690 NGC 5772 NGC 5806 NGC 5876 NGC 5908 NGC 5957 NGC 0980 NGC 6001 NGC 6014 NGC 6030 NGC 6085 NGC 6111 NGC 6126 NGC 6143 NGC 6155 NGC 6196 NGC 6464

Chapter 5

Cornparison Between Seyfert and

Control Galaxies

5.1 Introduction

With the analysis of the Seyfert and the control samples complete, a comparison

between their properties and the nearby environments of the galaxies can be un-

dertaken. This chapter will compare the two samples in t e m s of a wide variety of

parameters. Section 5.2.1 will describe the distribution of parameters related to the

seIection of the host galaxies based on redshift and luminosity. Section 5.2.2 will com-

pare the surface-brightness profile parameters from the isophotal analysis and discuss

the problems associated with multi-cornponent fitting. Section 5.3.1 will compare the

nearby environments of the hosts by examining properties of the optical cornpanion

galaxies found around the host galaxies. Section 5.3.2 will discuss the kequency with

which disturbed morphologies occur within the host galaxies. Finally, Section 5.4 will

summarize the comparison of the Seyfert galaxies and the control galaxies.

5.2 Distribution of Host Galaxy Properties

5.2.1 Host Galaxies

As mentioned in Chapter 1, the control galaxies were selected based on their redshift.

morphology, and luminosity. The foilowing histograms illustrate the distributions of

some of these properties. Al1 the histograms in this chapter follow the same format:

the x-axis (abscissa) is the parameter whose distribution is being considered, and the

y-axis (ordinate) shows the relative frequency of that parameter. The left panel shows

the relative frequency for al1 the data (Seyfert + control), the middle panel shows

the relative frequency for the Seyfert data (Seyfert 1 as a solid line, Seyfert 2 as a

dotted line), and the right panel shows the relative nequency for the control galaxy

data. The histograms have been normdized such that f dx = 1. The distributions

have been compared by using the Kolmogorov-Smimov (K-S) test in which the nul1

hypothesis is that the two properties being compared are from the same underlying

population. Mention will be made only if the K-S test rejects the nul1 hypothesis at

a coddence level of 95% or greater.

Figure 5.1 shows the distribution of redshifts of the hosts. As can be seen, the

redshift distributions of the Seyferts and control galaxies are similar, as also shown

by the K-S test. The distribution of distances calculated from Equation 2.12 (in units

of Mpc) can be seen in Figure 5.2.

The distribution of the apparent magnitudes of the hosts as measured by M.M. De

Robertis (Paper 1) with PPP can be seen in Figure 5.3. Using the distances to the

host gdaxy, the absolute magnitude of the galaxy is computed using Equation 2.13,

and the distribution of absolute magnitude can be seen in Figure 5.4. The K-S test

shows that the distributions are similar for both the Seyfert and control galaxies.

Rcdshifts of H o s t s [ z ]

Figure 5.1: Distribution of host galaxy redshift. Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

The distribution of ellipticities of the hosts are found in Figure 5.5. The dis-

tributions are similar as demonstrated by the K-S test, so any &ect caused by tilt

extinction will be present in both samples. Tilt extinction is being neglected since it

is difficult to rneasure and so is much less tractable to include.

As c m be seen fiom the basic properties of the host galaxies, a fair comparison

can be made between the two samples since the distributions are similar. Though

there are slight differences in the distributions of redshift and apparent magnitude

between the Seyfert 1s and 2s. a fair comparison can still be made.

Distances to Hosts [Mpc]

Figure 5.2: Distribution of host galaxy distances (distances are given in h-' Mpc). Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

Histogram of Host Apparent Magnitudes 4

Apparent Magnitude of Hosts

Figure 5.3: Distribution of apparent magnitudes of host galaxies. Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

Histogram of Host Absolute Magnitudes F - ' - . . ' . - - T - - + - x - - - ' - . - ' - - + - E - - . r - - ' - - - ~

4 f n l I l . - - - . 1 . . I l I f . . , ; . l . . . l t . . . . . . 1 . J

-24 -22 -20 -24 -22 -20 -24 -22 -20 Absolute Magnitude of H o s t s

Figure 5.4: Distribution of absolute magnitudes of host galaxies. Left panel: d l hosts. rniddle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

Ellipticity of Hosts ( c - b/a)

Figure 5.5: Distribution of ellipticities of host galaxies. Left panel: al1 hosts. middle panel: Seyferts (solid: Syl , dotted: Sy2). right panel: Control hosts.

5.2.2 Distribution of parameters from surface-brightness pro-

file fitting

This section presents the distribution of paramet ers measured from the 3-component

surface-brightness profile-fitting routines. Both the disk and bulge parameters d l

be shown. Figure 5.6 displays the distribution of the disk scde radii ro (in kpc),

and Figure 5.7 shows the distnbution of the bulge effective radii r, (in kpc) of the

host galaxies. The distribution of disk centrai surface brightness pd (mag/arcsec2)

can be seen in Figure 5.8, and the distnbution of bulge effective surface brightness 96

(mag/arcsec2) is presented in Figure 5.9.

Scalc radii [kpc]

Figure 5.6: Distribution of fitted scale radii ro (kpc). Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

The four parameters have a somewhat similar distribution for the Seyfert and

control hosts, as well as between the Seyfert 1s and 2s according to the K-S test,

except for the bulge radii (for which the Seyfert versus the control distribution is

rejected at the 97% level). The mean scale radii are (ro) = 5.2 f 0.7 kpc for the

Seyferts, and (ro) = 6.0 k 0.8 kpc for the control galaxies (the uncertainties given are

the rms of the mean). The mean disk surface brightness for both the Seyfert and the

Figure 5.7: Distribution of fitted effective radii re (kpc). Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

Histogram of Bulge effective radii 1 - - ' - - " -

control hosts are ( p d ) = 19.74k0.21 mag/arcçec2 and (pd) = l9.67& 0.22 rnag/arcsec2

respectively. The mean bulge effective radii are (7,) = 9.2 f 2.8 kpc for the Seyferts.

and (7,) = 8.6 f 1.8 kpc for the control galaxies. The mean bulge surface brightness

for both the Seyfert and the control hosts are (pb) = 20.71 f 0.48 mag/arcsec2 and

(pb) = 21.01 f 0.35 rnag/arcsecz respectively. The average fraction of luminosity

from the three components in the Seyfert galaxies was 54% from the disk, 40% from

the bulge, and 6% from the PSF. The control galaxies in cornparison, had average

luminosity fractions of 53% frorn the disk and 47% fiom the bulge. These similarities

indicate yet again that the control sample cm be fairly compared with the Seyfert

sample. The difference in the distribution of the bulge radii is noticeable for small r,

and arises since the bulge and the Gaussian PSF are difficult to distinguish between.

With multi-component non-linear fits, issues of confidence, numerical stability,

and uniqueness arise. Fitting a disk and bulge simultaneously is generally considered

relatively straightforward, whereaç fitting three components simultaneously carries

with it some rîsk. The three-component fitting 1 performed is indeed sensitive to the

- - . . - - --

A . . - - . - # . l ! O 10 20 O 10 20 O 10 20

Effcctivc radii [kpc]

Figure 5.8: Distribution of fitted disk surface brightness pd (rnag/arcsec2). Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

quality of the data and the initial "guesses" of the parameters, as the chi-squared

hypersurface can be complicated. With such a large parameter-space, there can be

many local minima in the hypersurface, and so it may be difficult to find the global

minimum. There are two further complications regarding the third component (the

PSF) in these fits:

1. The data from Ellipse starts a t 1.8 pixels from the intensity centroid. At that

radius, the PSF is typically down to 20% of its peak value, and so we are trying

to fit the lower-intensity %wingsn of the PSF.

2. For the inner pixels, the PSI? and bulge component are both very similar in

that they are strongly peaked at the center. Due to this, the parameters p ~ ,

w and r, are strongly correlated.

In order to test the stability and uniqueness of the three-component fits, they were

redone using an inner radius of 5 pixels using only bulge and disk components. A

Gaussian PSF is down to 2% or less peak intensity at that radius, so this is reaçonable.

It was found that the disk parameters are quite stable, but that the bulge parameters

Histogram of bulge surface brightness I m . - - - - . . ' . - - s - . ~ ~ - l ~ - - - ~ - - - ' - - ~ ' - - - ' - - I g - - - ' - - - ' - - - . . - - - - t

Figure 5.9: Distribution of fit ted bulge surface brightness pb (mag/arcsec2). Left panel: d l hosts- middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

show a fair arnount of variability in some galaxies.

There are obvious limitations to fitting three-component models in t his fashion.

though there are problerns with any procedure which fits parameters simultaneously.

An alternative empirical method of extracting the three components is to find a bright

unsaturated star on the image (a good PSF), and to subtract scaled versions of this

from the nucleus until some pre-determined criteria are met. In this manner the

PSF parameters are then known, and the resulting surface-brightness profile follows

a standard two-cornponent fit. We chose not to pursue this method both because it is

tirneintensive and because there is still a significant degree of subjectivity associated

with it.

Finally, I would like to note the frequency with which the PSF does not fit a t

all. The three-component fits were only performed for the Seyfert galaxy profiles:

where we expect to find a PSF component due to its bright star-like nucleus. Of

these fits, a PSF was recovered in 11 of 15 Seyfert ls, but only in 4 of 15 Seyfert 2s.

This is explainable by the observational evidence that Seyfert 1s are brighter than

Seyfert 2s (Yee l983), and thus it is more difficult to fit a PSF to Seyfert 2s. When

the alternative method of fitting the three components is performed the situation

becomes süghtly better, in which 12 of 15 Seyfert 1s and 8 of 15 Seyfert 2s were fit

with a PSF.

5.3 Distribution of Environmental Properties

5.3.1 Properties Derived from Cornpanion Galaxy Data

This section presents information regarding the companions around the host galaxies

and their "projected" properties. The first point 1 would like to stress is that these

galaxies are not necessarïly physical companions, some are optical, and thus the

projected separation distances are a minimum. For the 32 Seyfert hosts, 371 optical

cornpanion galaxies were found (averaging 11.6 companions/host ) , while for the 49

control hosts, 657 optical companions were found (averaging 13.4 companionç/host).

In order to provide a fair comparison between the two samples we will only consider

those galaxies which are within 200 kpc (projected distance); this ensures that the

comparison is being performed using companions within a similar radius in the rest

frame of the hosts. Within 200 kpc, 359 optical companions were found around the

Seyfert hosts (11.2 1.0 companions/host; Syl: 175, Sy2: 184), and 520 optical

cornpanions were found around the control hosts (10.6 f 0.9 companions/host. As in

the previous section, the uncertainties are the m s of the mean). Figure 5.10 shows

the relative fkequency of the number of companions around each host, and as the K-S

test shows, the distributions are similar for the two samples.

The distribution of projected separation distance from the companions to the host

Numbcr of Companion Galaxies

Figure 5.10: Distribution of the number of companion galaxies around the hosts. Left panel: d l hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

galaxies is presented in Figure 5.11 (in kpc). The K-S test shows that both distri-

butions are similar, though the Seyfert galaxies appear to have a slightly higher fre-

quency of companions within 50 kpc (which may be important tiddly). As would be

expected, the companions are found randomly with respect to position angle around

the hosts, as can be seen in Figure 5.12 (measured from North through East). AS the

histogram is binned into 45' intervals, one expects a Bat distribution with a relative

frequency of 0.125 in each bin, which one observes.

Based on the integrated flux of the companion galaxies, various magnitude and

luminosity parameters can be computed. The logarithm of the distribution of the

companion galaxies' apparent magnitudes is presented in Figure 5.13. Both samples

have a similar distribution as demonstrated by the K-S test, in which the relative

frequency of objects between 12 - 19 magnitude roughly follows a power-law, as one

expects from the luminosity function for galaxies (Schechter 1976). At a magnitude

of approximately R = +19 the distribution tums over and rapidly drops to zero,

Histogram of Separation Distances y

, - - -. -- ! . i , 1 - -- -- - -

- - --j i.... , . . _. / - - - I - 1 8

- -- - - - - J! ---

.. - - - 1 -- +... I - - - *

O 50 100 150 O 50 100 150 O 50 100 150 Separation dis tance (kpc)

Figure 5.11: Distribution of companion galaxy separation distances (in kpc). Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

indicating the magnitude at which incompleteness sets in and thus the limiting mag-

nitude to which 1 could detect faint companion galaxies efficiently. This illustrates

that the galaxy counts are roughly complete d o m to 19th magnitude, after which

the counts are incomptete. The magnitude difference between the host galaxy and

its companion galaxies can then be computed via Lp - Rhost, and the distribution

of Am can be seen in Figure 5.14. Again, both the Seyfert and control companion

distributions are similar (though the nul1 hypothesis is rejected a t the 99.9% level for

cornpaxison between the Seyfert 1s and 2s). There are differences between the Seyfert

1s and 2s in that the Seyfert 2s have an excess of companions in the Am = 5.5 - 7

range, while the Seyfert 1s have an excess of companions in the Am = 7 - 9 range.

Using the distances to the host galaxies, the absolute magnitudes of the companions

can be calculated (based on the assumption that the companion galaxies are located

at the same distance from us as the host). The distribution of the projected absolute

magnitudes of the companion galaxies is presented in Figure 5.15; to a first approx-

imation the Seyfert and control companions have a similar distribution, though the

Histogram of Companion Position Angles

Posi Lion Angle of Companion

Figure 5.12: Distribution of Position Angle of companions with respect to host [North through East]. Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

differences between the Seyfert 1s and 2s (as noted with the Am parameter), are

apparent in this parameter as well (Seyfert 1s and 2s distribution rejected at the 98%

level) .

Now that the "absolute" magnitudes of the companions galaxies have been cal-

culated, their luminosities can be computed. Using Ma = -22.1 (Schechter 1976)

which is equivalent to L*, the distribution of companion galaxy iuminosities can be

seen in Figure 5.16. R o m the luminosity, the "tidal" parameter for each compan-

ion galaxy can be calculated as described in Section 2.4.6. Figure 5.17 contains the

distribution of the individual companion galaxy tidal parameters, and Figure 5.18

presents the distribution of the cumulative tidal parameter Q = C Qi for each host

galaxy. The K-S test shows that the distribution of Qi is similar for both the Seyfert

and control companion galaxies, a s is also the case for Q. Unlike the distribution

absolute magnitude, the Seyfert 1s and 2s companions have similar distributions of

the tidal parameter according to the K-S test. There are, however, a few hosts (both

samples) in which Q > 105 L * / M pc3, consisting of severely disturbed systems (Seyfert:

Apparcnt Magnitude of Cornpanions

Figure 5.13: Distribution of apparent magnitudes of the companion galaxies. Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

NGC 5256, NGC 5929, NGC 6104. Control: UGC 10407, UGC 11865, UGC 3492,

and NGC 5541).

As seen with al1 the parameters related to the optical cornpanions of the host galax-

ies, the environments of Seyfert galaxies and the control galaxies are fairly similar.

There is a difference in the distribution of faint galaxies around Seyfert 1s compared

to Seyfert 2s, though when considered together, the Seyfert and control companion

distributions are similar. There is also no obvious difference in the tidal infiuences

the cornpanion galaxies have on the hosts, though both sarnples have their share of

very tidally disturbed systems (- 8 %) .

Histogram of A m a g between Host and Cornpanion - .-. I ! . . . . . . P ' . - ' , : 8 . . ; i : i

r ! i 7 8

A m (companion - host)

Figure 5.14: Distribution of Amag between host galaxy and companion galaxies (RmP - Rhost). Left panel: dl hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

Absolute Magnitude of Cornpanions

Figure 5.15: Distribution of absolute magnitudes of the cornpanion galaxies (assuming distance same as that of host). Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

Histogram of Companron Luminosities -L - . - '

0.0001 o.mi a o i ai I

Lum inosi ty of Cornpanions [L*]

Figure 5.16: Distribution of companion galaxy luminosities (L* ) . Left panel: dl hosts. middle panel: Seflerts (solid: Syl, dotted: Sy2). right panel: Control hosts.

iiistogram of Companlon Tidal Influence

L.

6

4 0.2 s C

O

a. a2 L. )ii

d

a2 L

Tidal influence of Cornpanions [L*/Mpc3]

Figure 5.17: Tidal parameters of the companion galaxies. Left panel: dl hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

Histogram of Host Tidal Influence - - - . f -

(CQ,)Summed Tidal Influence of Hosts [Le/Mpc3]

Figure 5.18: Summed tidal parameters of the cornpanion galaxies for the hosts (Q = CQi). Left panel: al1 hosts. middle panel: Seyferts (solid: Syl, dotted: Sy2). right panel: Control hosts.

5.3.2 Host Galaxy Morphological Disturbances

Light asymmetries and rnorphological disturbances of the host galaxies are another

aspect of the environment of the host galaxies which can be examined. There are

various rnorphological features which m a y be a symptom of a recent interaction or

rnerger or evidence for a radial Bow of material.

As mentioned earlier, bars are thought to be an efficient mechanism of transporting

gas to the inner regions of a galaxy, thus fueling a possible AGN (Athanassoula 1992;

Shlosrnan and Noguchi 1993). As such, it is instructive to note the frequency of bars

in the host galaxies. Rings can be a symptom of a recent interaction in which a

cornpanion object passes right through the host galaxy (e.g., Combes et al. 1991).

Any other forrn of distortion or disturbance in the galaxy may also be a sign of some

kind of interaction, and may appear as tidal tails, bridges, prominent dust lanes,

or other significant light asymmetries. Another sign of a recent interaction may be

extreme twisting of isophotes (Le. position angle profile changes by a large arnount,

say 45'). Tables 5.1 and 5.2 show the frequency of rnorphological disturbances in

both the Seyfert host and the control host respectively detected in this analysis. -4

(J) indicates that the feature was noticed in the galaxy, and (t) indicates that a

partial feature was observed. A "B" shows the presence of bars in the host galaxy,

an "R" rings, a "D" distortions of some other variety, "Q", illustrates which galaxies

have position-angle profiles which have "excursions" of more than 45', and finally, an

"A" shows the occurrence of any of the previous disturbances (i.e. bar and/or ring

and/or distortions) .

Table 5.3 summarizes the frequency of bars, rings, and other distortions. It

presents the number of galaxies containing the feature (including partial features

in parentheses) as well as the fraction of galaxies with that feature. As can be seen,

Table 5.1: Seyfert hosts: Bars, rings and distortions Name B R D 8 A

blrk 0231 Mrk 0461 Mrk 0471 Mrk 0789 Mrk 0817 Mrk 0841 UGC 06100 UGC 08621 NGC 3080 NGC 3227 NGC 3362 NGC 3516 XGC 3718 NGC 3786 XGC 3982 SGC 4051 YGC 4151 XGC 4235 NGC 4253 NGC 4388 NGC 5252 NGC 5256 NGC 5273 NGC 5283 NGC 5347 NGC 5548 NGC 5674 NGC 5695 NGC 5929 NGC 5940 NGC 6104 NGC 6814

J 4 J J J J J

J J J t t

UGC 05734 UGC 07064 UGC 09295 UGC 10097 UGC 10407 UGC 11865 IC 875 IC 1141 NGC 3169 NGC 3492 NGC 3756 NGC 3825 NGC 3938 NGC 3968 NGC 4045 NGC 4048 NGC 4088 NGC 4172 NGC 4224 NGC 4352 NGC 4375 NGC 4477 NGC 4799 NGC 4944

Table 5.3: E

Table 5.2: Control hosts: Name B R D 8 A

Bass Rings Dist . e

Bars, rings and distortions Name B R D 8 A

- NGC 4954 NGC 5289 J J NGC 5375 J NGC 5505 d NGC 5515 t NGC 5541 d NGC 5603 NGC 5644 NGC 5690 J NGC 5772 NGC 5806 t NGC 5876 J J l/ NGC 5908 t NGC 5957 J J NGC 5980 NGC 6001 t d NGC 6014 t t l / NGC 6030 NGC 6085 NGC 6111 NGC 6126 NGC 6143 d NGC 6155 d NGC 6196 NGC 6764 J

ieauencv of bars rings and distortions Control

# % 12(18) 24(37) 4(7) 804)

ll(13) 22(27) 11 22

26(31) 53(63)

there are slightly different ratios of galaxies that contain bars or rings in both sarn-

ples. However, a large fraction of the galaxies in both samples contain some form

of disturbance, though a slightly larger fraction of Seyfert galaxies contain a distur-

bance. This indicates that the environments of Seyfert galaxies are similar to control

galaxies in t e m s of possible morphological disturbances.

A summary can now be made regarding the properties and the environment of Seyfert

galaxies as compared to control sample of galaxies. As seen in previous sections,

the Seyfert galaxies and the control galaxies were selected to have similar redshifts,

morphologies, and luminosities. These two samples of galaxies were then found to

have similar surface photometry paramet ers resulting fiom the isophotal analysis,

indicating that a fair comparison can be made between the two samples. The Seyfert

and control hosts were also seen to be in similar environments with regard to the

number of optical cornpanion galaxies, and their corresponding projected luminosities

and tidal influence. Finally, we saw that both sets of galaxies are dso very similar

in that the same fraction contains some form of morphological disturbance. The

concluding chapter will attempt to address these sirnilanties in terms of the Unified

Mode1 and the interaction b o t hesis.

Chapter 6

Conclusions

In studying 32 Seyfert galaxies and a control sample of 49 non-active galaxies, we

sought to test the interaction mode1 for activity in galactic nuclei. The AGN "engine"

consists of the accretion of material onto a supermassive black hole. The interaction

hypothesis describes the mechanism by which the fuel reaches the accretion disk and

central engine. This model proposes that material is transported to the inner region

of the galaxy Ma a perturbing interaction (either a tidal perturbation or a cannibalis-

tic merger). In this model, Seyfert galaxies should then have an excess of companion

galaxies as cornpared to normal galaxies. In testing this hypothesis, this thesis ex-

amined the morphoIogies and optical companion galaxies of Seyfert galaxies and a

controi sarnple of normal galaxies in order to compare the environments of Seyîert

galaKies to that of normal galaxies, and found that the environments are similar.

The two samples were matched in redshift, morphological clas, and luminosity in

order to minimize any biases that may arise due to unknown selection effects, and the

host-galaxy properties were then examined to determine if a fair cornparison could

be made between the two samples.

The process of investigating the nearby environments of the galaxies involved sev-

eral steps. The surfacebrightness profiles were measured using the elliptical isophotal

routines in IRAF, which were then fit with a disk and a bulge component (and a Gaus-

sian PSI? in the case of the Seyfert galaxies). Optical companions were then visudly

searched for and their relevant parameters were measured (i.e. position and appar-

ent magnitude). Finally, unusual host-galaxy morphologies were examined by visual

inspection and using unsharpmasking techniques to find features such as bars and

rings.

The surface-brightness profile-fitting parameters for the Seyfert and control galax-

ies were compared. The radial and intensity parameters (r0, r,, pd, and pb) were

found to have similar distributions in the two galaxy samples, thus indicating that

the control sample is a fair one. It was acknowledged that the three-component fit-

ting technique used for the Seyfert galaxies can be problematic and that there may

be better ways of achieving more consistent fits. As expected, however, Seyfert 1s

were much more successful a t having the nuclear component fit, which confirms ob-

servations that Seyfert 1s have a more dominant nucleus than Seyfert 2s. Other than

this difference, the other surface brightness profile parameters were similar for both

the Seyfert 1s and 2s.

Similarities were also found in the environments of the sample galaxies via corn-

panion galaxy counts. Counts of optical cornpanion galaxies around the host galaxies

resulted in an average of 11.2 & 1.0 companions/Seyfert galaxy and 10.6 f 0.9 corn-

panions/control galaxy when a maximum search radius of 200 kpc was imposed. The

distributions of the various parameters derived from the companions were similar for

both the Seyfert and the control samples, which included angular distribution, appar-

ent and absolute magnitudes, luminosities, and maximal tidal influence. The similar-

ity in these parameters indicates that the nearby environments of Seyfert galaxies are

similar to that of the control galaxies. One difference was noted, however; Seyfert 1s

and 2s had somewhat different distributions of Am (difference in apparent magnitude

between the companion galaxies and their hosts), although it is not known whether

this is signifiant in terms of the interaction hypothesis. Unlike Paper II7 it was found

that Seyfert 1s and 2s had a similar number of companion galaxies (perhaps because

this companion search went 2 6 magnitudes dimmer than the host galaxies).

The frequency of disturbed morphologies such as bars, rings, and position angle

excursions was also examined. It was found that the control galaxies had roughly

the same fraction of disturbed galaxies as did the Seyfert sample. The fraction of

"disturbed" galaxies was found to be roughly 213 for the control sample and 314

for the Seyfert sample. This is another indication that the environments of Seyfert

galaxies are roughly similar to normal galaxies, just as in Paper II, which finds that

Seyfert galaxies are not found in richer environments as compared to the control

sample.

Based on this analysis, Seyfert galaxies and the control galaxies occupy similar

environments, and exhibit a similar frequency of disturbances. This similarity has a

few implications for the interaction hypothesis. Since the Seyfert galaxies and the

control galaxies occur in similar environments this could indicate that galaxy-galaxy

interactions do not necessarily initiate activity in AGNs but, rather, rnay contribute

to increased star formation in the host (e.g., Larson and Tinsley 1978). This is not

to Say that perturbing interactions do not initiate activity, but rather these rnay not

be necessary, and that there may be other mechanisms which are not yet understood

that can also lead to activity. If there is not enough material being transported to

the innermost region of the galaxy due to a perturbing interaction then there will

not be any activity; though if material does get to the inner parsec there will be

activity provided a SBH exists. There are Seyfert galaxies that do not appear to be

morphologically dist urbed, so t here may be alternat ive mechanisrns for transport ing

gas to the inner galaxy and thus initiating activity Clearly. the interaction mode1

needs to be studied in more detail to determine whether it is reasonable hypothesis,

or whether the theory needs to be modified. One suggestion put forth by Paper II is

that "minor rnergers" may play an important role in the activity of low-luminosity

AGNs such as Seyferts, since minor mergers should occur more fiequently than major

interactions and can drive a sufficient quantity of fuel into the central region of the

host.

More research needs to be done in the area of Seyfert galaxies and their environ-

ments since there is no clear consensus yet regarding the interaction hypothesis. In

order to accomplish this, one should acquire higher resolution images in several pas-

bands of a large nurnber of Seyfert galaxies and control galaxies (using the adaptive

optics bonnet a t CFHT perhaps) in order to detect very small and close distur-

bances. Using a large sample of galaxies will improve the statistical uncertainties.

thus sharpening the cornparison between the two samples. Multiple-colour images

provide information on the nature of the galaxies (such an analysis is currently in

progress using two colours, B and R, by S. Virani). Higher quality surface-brightness

profiles could then be extracted from the data and several methods of radial profile

fit ting could t hen b e used (simultaneous t hree-component fitting, two-component fit-

ting, and PSF subtraction followed by two-component fitting) to acquire consistent

results. The search for optical companion galaxies could then be undertaken via vi-

sua1 inspection as well as using an automated technique (with human intemention)

in order to accurately determine the properties of these objects. Spectra could also

be obtained of the host galaxies and their optical companion galaxies in order to fur-

ther clasçify the objects and get their redshifts. In this way, distances to the optical

companions could be computed, and it can be determined whether the objects are ac-

tually physical companion galaxies. Moreover, the kinematics and dynamics of these

systems could also be determined. Explicit knowledge of the physical companions

could then be used to calculate more accurate tidal forces that these objects have

on the hosts. -4lso required is an improved understanding of the theory behind the

interaction hypothesis (e-g., incorporating dissipative i d o w of gas into the centers

of galaxies via stellar and gaseous bars) so that the observations more closely match

t heory.

In closing, there is much research that must be undertaken before we can full-

understand AG&, which involves detailed observations of the nearby and large-scale

environments of these galaxies as well as the examination of the galaxies themselves.

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Appendix A

Programs Used for Analysis

A.1 )r IRAF Packages

Image Reduction and Analpis Facility (IRAF) is a commonly used softwaxe package

in astronorny. What follows are descriptions of the important routines (Imexamine,

Ellipse, Imedit , Imar i th , Gauss) used during the reduction and analysis. -41~0

provided are an example of the important parameters used while executing each task.

A.I.1 Imexamine

The imexamine task is used to determine statistical information about image sec-

tions. The statistics tool (m key) retums the mean, standard deviation, maximum

and minimum within a n x n pixel box (we have set n = 5), and is useful for deter-

mining properties such as the background sky level and noise. Surface plots (s) and

contour plots (e) in a 15x15 pixel box are a convenient way of looking at the data.

A very important tool is the radial profile tool (r), which is a very flexible tool since

the radius to which data is measured is completely configurable by the user. This

tool locates the nearest peak to the image cursor, then determines the centroid of this

peak, plots a radial profile of the data around this point, and fits a Gaussian to this

profile returning numerous parameters (centroid, FWHM, peak, ellipticity, position

angle, and integrated flux). Below are the parameter lists for the imexamine task as

well as the parameter list for radial profile sub-task (rimexamine).

Imexamine parameters input = "n6764rU images t o be exambed

(logf i l e = "imexam. logu) l o g f i l e (ncstat = 5) number of columns f o r s t a t i s t i c s (nistat = 5) number of l i n e s f o r s t a t i s t i c s

(use-display = yes) enable d i r e c t display in terac t ion

Rimexamine paramet ers (xlabel = "Radius" ) (ylabel = "Pixel Value")

(f i t p l o t = yes) (center = yes)

(background = yes) (radius = 7.) (buffer = 1.)

(width = 2.) (xorder = 4) (yorder = 4) ( rp lo t = 9.)

X-axis l abe l Y-axis l abe l Overplot gaussian f i t ? Center object i n aperture? F i t and subtract background? Ob j e c t radius Background buf f e r width Background vidth Background x order Background y order Plot t ing radius

The E l l i p s e task contained in the Isophote package of the STSDAS (Space Telescope

Science Data Analysis System) package fits elliptical isophotes to an image. Details

of the algorithm were described in Section 2.4.2 and the important fitting parameters

are listed below.

El l ipse parameters input = "n3982"

output = "gal. tab" a0 = 8.4

mina = 1.7 mkxa = 53.

(harmonies = ''none" ) (x0 = INDEF) (y0 = INDEFI

(epsO = ZNDEF) ( te ta0 = SNDEFI

(hcenter = yes) (heps = no)

input Mage name output t ab le name i n i t i a l semi-major axis minimum semi-major axis maximm semi-major a i s opt ional harmonic numbers i n i t i a l e l l ipse center

i n i t i a l e l l i p t i c i t y i n i t i a l posi t ion angle hold center f ixed ? hold e l l i p t i c i t y f ixed ?

( h t e t a = no) (astep = 0.1) (linear = no) (minit = 15) ( a i t = 100)

( l s lope = 0 .) (conver = 0 .)

( c l i p = O .O21 (marrit = LNDEF)

(integrmode = 'bi-linear")

hold posi t ion angle f ixed ? s t e p betveen successive e l l i p s e s linear as tep ? minimiin no. of i t e ra t ions maximun no. of i t e ra t ions l i m i t f o r acceptable slope convergency sens i t iv i ty control f r a c t i o n of points t o clip off max. semi-major axis f o r i t e r a t i v e mode azea in tegra t ion mode

A.1.3 Imedit

The imedit task can be used to delete unwanted stars and ion events as weU as

touch-up other defects in the image. This task is performed interactively in real time

so the user can see the changes as they are being done. The main tool in this task is

the background replacement routine. With this routine, the user specifies the radius

of a circular aperture which is surrounded by circular annulus. The pixels within

the aperture are then replaced by a background surface based on the pixels in the

annulus; Gaussian noise is added to the replacement pixels. The polynomiai order of

the background surface is set by the user, and was set to 3rd-order for this research.

Imedit parameters input = "n3169r1' Images t o be edi ted

output = "-113169" Output images (aperture = "ci rcuiar") Aperture type

(radius = 4. ) Subst i tu t ion radius (search = 0. ) Search radius (buffer = 2.) Background buf f e r vidth (uidth = 2.) Background vidth

(xorder 4) Background x order (yorder = 4) Background y order (value = 0 .) Constant value subs t i tu t ion (sigma = 6.6) Added noise sigma

(conmiand = "display $image 1 erase=$erase fill=yes order=O >& dev$nullM) Display command

A.1.4 Imarith

The imarith task is used to perform image arithrnetic. This can either be accom-

plished with an image and a constant or with two images. In the case of two images,

the specified operation is performed an a pixel-tepixel basis (similar to matrix addi-

tion and subtraction. though it applies to multiplication and division as well). This

task is useful for removing the background sky level from an image, as well as dividing

an image by a smoothed image for unsharpmasking.

Imarith parameters operandl = "n61lir2" Operand image or numerical constant

OP = 'y Operat or operand2 = "n6111gau" Operand image or numerical constant

result = I1lpfn Resultant image

A.1.5 Gauss

The Gauss task convolves an image with a flux-preserving Gaussian kernel in which

the width a is specified by the user. This task is useful for unsharp-masking, as well

as for smoothing images in general.

Gauss parameters input = "orig"

output = "gau" sigma = 4.434

(ratio = 1.) (theta = 0.) (nsigma = S . )

(bilinear = yes)

Input images t o be fit Output images Sigma of Gaussian along major ax i s of e l l i p s e Ratio of sigma i n y t o x Position angle of e l l i p s e Extent of Gaussian kernel in sigma Use bilinear approximation t o Gaussian kernel

A. 2 User-Supplied Programs

These are programs the author wrote to perform surface-brightness profile fitting and

to cornpute the many host and companion galaxy parameters.

A.2.1 galprof and s p l i t p r o f

Galprof and sp l i tprof fit analytic functions to the radial surface-brightness profiles

of galaxies (i.e. after they have been fit with ellipse). The main chi-squared minimiza-

tion routine is based on the algorithm in Numen'cul Reczpes by Press et al. (1992).

The algorithm fits an analytic function with unknown parameters to a data set, ad-

justing the parameters until the chi-squared reaches a minimum. The function used

for the galaxy surface-brightness profiles is found in Equation 2.10. The algonthm

also requires the first derivatives of the parameters in order to adjust the parameters

during each iteration such that the chi-squared decreases. These derivatives have the

following functional form: - -

The program splitprof takes the output parameters from gaiprof and creates

a data-file that contains the flux that is contnbuted by each of the three components

(disk, bulge, and Gaussian PSF). When the altemate two-component fitting is per-

formed on the Seyfert data, sp l i t p ro f is modified to cornpute the contribution by

the Gaussian PSF by integrating the flux left over between 1.8 pixels and 5.2 pixels.

This is accomplished

given by :

by first realizing that the flux in a Gaussian PSF annulus is

where a and b are the inner and outer radii of the aanulus. Thus the parameter in

question is given by: n

where F,,, is computed from the data via numerical integration using the trapezoidal

method:

where h, = ri+l - ri and f, = 2îrriIi where li is the "left over" flux and rl = a and

r,,, = b. Thus the PSF parameter can be computed by integrating the data-points

and substituting the result into Equation A.8.

A.2.2 raddist

This program cornputes various statistics about the host galaxies and its compan-

ion galaxies. This program correlates the companion galaxy files with the gdaxy

information files to produce various quantities such as apparent magnitude, abso-

lute magnitude, luminosity, separation distance, and tidal influence of the companion

galaxies, as well as the distance, luminosity, surface brightness, and the fraction of

luminosity due to each component for each of the host galaxies.

The fiaction of light contributed from each component is computed by first cal-

culating the integrated flux (out to a maximum radius rn) of each component. This

is given by:

which corresponds to the following for the Gaussian PSF, the disk, and the bulge:

where a = 7.688 and y = a ( r n / ~ , ) ' / ~ . The fractional luminosity is then computed by

dividing the component's flux by the total flw (FPr + FdiSk + &@)a The other parameters output by this program are computed as outlined in Chap

ter 2.4.6, at which point they can be compared as in Chapter 5.

Appendix B

Ellipt icity and Position Angle Plots

What folIows are the ellipticity profiles and the position-angle profiles for the host

galaxies of both the Seyfert and control samples. The data were provided by the

ellipse taçk in IRAF. Ellipticity is given by E = 1 - b/a and position angle is given

as from North through East.

B.1 Seyfert Data Set

The plots for the Seyfert samples are presented in Figures B.1 through Figures B.8.

B.2 Control Data Set

The plots for the control samples are presented in Figures B.9 through Figures B.21.

Pli-

* * Hn

km

W I W I Hn

".z,

1 I 1 1 1 1 I I I 1

10, FI

in- - - HC(

n- - HH - HW

U- - M - 0-

- Ht-I * * - O N

O

c---ie---i HH - O-: +

O r ' = ' HH , O N

4- - - 1 m CD- - I HH

L Hti I

-C w

I m H« m , O f rl

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